The following information is from The Urantia Book, Paper 47, "The Seven Mansion Worlds," Section 2, "The Probationary Nursery."

47:2.1 The infant-receiving schools of Satania are situated on the finaliter world, the first of the Jerusem transition-culture spheres. These infant-receiving schools are enterprises devoted to the nurture and training of the children of time, including those who have died on the evolutionary worlds of space before the acquirement of individual status on the universe records. In the event of the survival of either or both of such a child’s parents, the guardian of destiny deputizes her associated cherubim as the custodian of the child’s potential identity, charging the cherubim with the responsibility of delivering this undeveloped soul into the hands of the Mansion World Teachers in the probationary nurseries of the morontia worlds.

47:2.2 It is these same deserted cherubim who, as Mansion World Teachers, under the supervision of the Melchizedeks, maintain such extensive educational facilities for the training of the probationary wards of the finaliters. These wards of the finaliters, these infants of ascending mortals, are always personalized as of their exact physical status at the time of death except for reproductive potential. This awakening occurs at the exact time of the parental arrival on the first mansion world. And then are these children given every opportunity, as they are, to choose the heavenly way just as they would have made such a choice on the worlds where death so untimely terminated their careers.

47:2.3 On the nursery world, probationary creatures are grouped according to whether or not they have Adjusters, for the Adjusters come to indwell these material children just as on the worlds of time. Children of pre-Adjuster ages are cared for in families of five, ranging in ages from one year and under up to approximately five years, or that age when the Adjuster arrives.
Comment. Adjusters reach their human subjects on Urantia, on the average, just prior to the sixth birthday. In the present generation it is running five years, ten months, and four days. [UB 108:2:1]

47:2.4 All children on the evolving worlds who have Thought Adjusters, but who before death had not made a choice concerning the Paradise career, are also repersonalized on the finaliter world of the system, where they likewise grow up in the families of the Material Sons and their associates as do those little ones who arrived without Adjusters, but who will subsequently receive the Mystery Monitors after attaining the requisite age of moral choice.
Comment. The Material Sons are the Adams and Eves such as our Adam and Eve.

47:2.5 The Adjuster-indwelt children and youths on the finaliter world are also reared in families of five, ranging in ages from six to fourteen; approximately, these families consist of children whose ages are six, eight, ten, twelve, and fourteen. Any time after sixteen, if final choice has been made, they translate to the first mansion world and begin their Paradise ascent. Some make a choice before this age and go on to the ascension spheres, but very few children under sixteen years of age, as reckoned by Urantia standards, will be found on the mansion worlds.

47:2.6 The guardian seraphim attend these youths in the probationary nursery on the finaliter world just as they spiritually minister to mortals on the evolutionary planets, while the faithful spornagia minister to their physical necessities. And so do these children grow up on the transition world until such time as they make their final choice.

47:2.7 When material life has run its course, if no choice has been made for the ascendant life, or if these children of time definitely decide against the Havona [and Paradise] adventure, death automatically terminates their probationary careers. There is no adjudication of such cases; there is no resurrection from such a second death. They simply become as though they had not been.

47:2.8 But if they choose the Paradise path of perfection, they are immediately made ready for translation to the first mansion world, where many of them arrive in time to join their parents in the Havona ascent. After passing through Havona and attaining the Deities, these salvaged souls of mortal origin constitute the permanent ascendant citizenship of Paradise. These children who have been deprived of the valuable and essential evolutionary experience on the worlds of mortal nativity are not mustered into the Corps of the Finality.

     It is apparent from the following Scriptures in the Book of Revelation that Christians are confused regarding the definition of the second death.
Revelation 2:11 He that hath an ear, let him hear what the Spirit saith unto the churches; He that overcometh shall not be hurt of the second death.
Revelation 20:6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
Revelation 20:14 And death and hell were cast into the lake of fire. This is the second death.
Revelation 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.

     Upon attaining Paradise and the Deities, these salvaged souls of mortal origin constitute the permanent ascendant citizenship of Paradise. These children who have been deprived of the valuable and essential evolutionary experience on the worlds of mortal nativity are not mustered into the Corps of the Finality.
Comment. The Corps of the Finality is the destination of most mortals who complete the age-long training course in universe administration.

     The following information is from The Urantia Book, Paper 47, Section 1, "The Finaliters' World."

47:1.4 On the first mansion world all survivors must pass the requirements of the parental commission from their native planets. The present Urantia commission consists of twelve parental couples, recently arrived, who have had mortal experience in rearing three or more children to the pubescent age. Service on this commission is rotational and is for only ten years as a rule. All who fail to satisfy these commissioners as to their parental experience must further qualify by service in the homes of the Material Sons [and Daughters] on Jerusem or in part in the probationary nursery on the finaliters’ world.

47:1.5 But irrespective of parental experience, mansion world parents who have growing children in the probation nursery are given every opportunity to collaborate with the morontia custodians of such children regarding their instruction and training. These parents are permitted to journey there for visits as often as four times a year. And it is one of the most touchingly beautiful scenes of all the ascending career to observe the mansion world parents embrace their material offspring on the occasions of their periodic pilgrimages to the finaliter world. While one or both parents may leave a mansion world ahead of the child, they are quite often contemporary for a season.

47:1.6 No ascending mortal can escape the experience of rearing children—their own or others—either on the material worlds or subsequently on the finaliter world or on Jerusem. Fathers must pass through this essential experience just as certainly as mothers. It is an unfortunate and mistaken notion of modern peoples on Urantia that child culture is largely the task of mothers. Children need fathers as well as mothers, and fathers need this parental experience as much as do mothers.

     The following information is from The Urantia Book, Paper 45, Section 6, "Adamic Training of Ascenders."

45:6.4 No surviving mortal, midwayer, or seraphim may ascend to Paradise, attain the Father, and be mustered into the Corps of the Finality without having passed through that sublime experience of achieving parental relationship to an evolving child of the worlds or some other experience analogous and equivalent thereto. The relationship of child and parent is fundamental to the essential concept of the Universal Father and his universe children. Therefore does such an experience become indispensable to the experiential training of all ascenders.

45:6.5 The ascending midway creatures and the evolutionary seraphim must pass through this parenthood experience in association with the Material Sons and Daughters of the system headquarters. Thus do such nonreproducing ascenders obtain the experience of parenthood by assisting the Jerusem Adams and Eves in rearing and training their progeny.

45:6.6 All mortal survivors who have not experienced parenthood on the evolutionary worlds must also obtain this necessary training while sojourning in the homes of the Jerusem Material Sons [and Daughters] and as parental associates of these superb fathers and mothers. This is true except in so far as such mortals have been able to compensate their deficiencies on the system nursery located on the first transitional-culture world of Jerusem.

45:6.7 This probation nursery of Satania is maintained by certain morontia personalities on the finaliters’ world, one half of the planet being devoted to this work of child rearing. Here are received and reassembled certain children of surviving mortals, such as those offspring who perished on the evolutionary worlds before acquiring spiritual status as individuals. The ascension of either of its natural parents insures that such a mortal child of the realms will be accorded repersonalization on the system finaliter planet and there be permitted to demonstrate by subsequent freewill choice whether or not it elects to follow the parental path of mortal ascension. Children here appear as on the nativity world except for the absence of sex differentiation. There is no reproduction of mortal kind after the life experience on the inhabited worlds.

45:6.8 Mansion world students who have one or more children in the probationary nursery on the finaliters’ world, and who are deficient in essential parental experience, may apply for a Melchizedek permit which will effect their temporary transfer from ascension duties on the mansion worlds to the finaliter world, where they are granted opportunity to function as associate parents to their own and other children. This service of parental ministry may be later accredited on Jerusem as the fulfillment of one half of the training which such ascenders are required to undergo in the families of the Material Sons and Daughters.

45:6.9 The probation nursery itself is supervised by one thousand couples of Material Sons and Daughters, volunteers from the Jerusem colony of their order. They are immediately assisted by about an equal number of volunteer midsonite parental groups who stop off here to render this service on their way from the midsonite world of Satania to the unrevealed destiny on their special worlds of reservation among the finaliter spheres of Salvington.