JOEL - First of all, everyone who is resurrected will come forth with a body at the same stage of growth as it was when they were laid to rest, as Joseph Smith explained,

"All men will come from the grave as they lie down, whether old or young" (TPJS, p. 199).

Joseph F. Smith also added:
"The body will come forth as it is laid to rest, for there is no growth nor development in the grave. As it is laid down, so will it arise, and changes to perfection will come by the law of restitution. But the spirit will continue to expand and develop, and the body, after the resurrection will develop to the full stature of man" (Joseph F. Smith, IE 7 [June 1904]:623-24).

We know that all children who die before the age of 8 years are saved in the Celestial Kingdom (D&C 137:10) and will therefore come forth in the morning of the first resurrection(D&C 88:97-98). If their righteous parents also come forth at that time, they will most definitely be able to raise them during the Millennium.
Joseph Smith taught that the infant child that was laid away in death would come up in the resurrection as a child; and, pointing to the mother of a lifeless child, he said to her: “You will have the joy, the pleasure, and satisfaction of nurturing this child, after its resurrection, until it reaches the full stature of its spirit.” (Gospel Doctrine, 455-56)
I am certain that wherever possible, God will make sure that the parents of those children are resurrected sometime before or at least at the same time the child is.
Also, since all children who die before the age of accountability are guaranteed the Celestial Kingdom, they will never be tested or tempted by Satan. Joseph Fielding Smith said,
“Satan cannot tempt little children in this life, nor in the spirit world, nor after their resurrection. Little children who die before reaching the years of accountability will not be tempted.” (Doctrines of Salvation, 2:56-57.) That will make raising them a lot easier.
However, if the parents come forth later in the first resurrection (inheritors of the terrestrial kingdom, D&C 88:99) or at the last resurrection at the end of the Millennium (telestial kingdom, D&C 88:100), their righteous children will of course have to be raised by someone else.

KEN - The question for me still remains: When children are resurrected, are they resurrected with the full knowledge they had while in Spirit World? So if a three-year-old was resurrected would he still have the intellect of a three-year-old or would his intellect match that of his Spirit? If it matched his Spirit, then what need would he have of being "raised"? He could be together with his parents, but they wouldn't really have a need to raise him, since he may even be further progressed (Spiritually) then the parents.

JOEL - Here are some things President Joseph Fielding Smith said:
“We were all mature spirits before we were born; and the bodies of little children will grow after the resurrection to the full stature of the spirit, and all the blessings will be theirs through their obedience, the same as if they had lived to maturity and received them on the earth. There is restitution, there is growth, there is development, after the resurrection from death.” (Gospel Doctrine, pp. 455-56.)

So according to Joseph Fielding Smith there will still be growth, development, and the requirement for obedience to the laws of the Gospel for these children who died before the age of accountability. Even though their spirits are pure and righteous their physical minds will still need to be educated so they can learn and understand the Gospel as they grow. But they will have no desire to commit sin nor will they have any need to be tested or tempted as I said earlier. And their bodies will still need to continue to grow, which I assume will require some kind of nourishment. They will still need parents who can provide them with food, clothing, and a place to live.

Isaiah said of the Millennium,
"And they shall build houses, and inhabit them; and they shall plant vineyards, and eat the fruit of them,…and mine elect shall long enjoy the work of their hands" (Isa. 65:21-22)
So in many ways, life will be much as it is now, except that everything will be done in righteousness.

You ask if they will have full knowledge of everything they knew while in the spirit world before they were resurrected. I believe their spirits will have the knowledge but their minds and bodies will need time to catch up to it before that knowledge can be made fully manifest in them. So this means that a three-year-old will still have the intellect of a three-year-old. He will still need parents who can teach him how to read and write and communicate with others. Then as he gradually approaches his full stature physically, he may be able to "remember" everything he knew in the spirit world. This is speculation on my part, however. Our prophets and scriptures have never really fully described all the specifics of how it all works. As Joseph Smith said about the resurrected body, "No man can describe it to you—no man can write it" (TPJS, p. 368).

Could the child be more fully progressed(spiritually) than the parents? I suppose it is possible, if the parents had not already died and been resurrected yet before the child did. However, the Prophet Joseph Smith taught that all beings "who have tabernacles (bodies), have power over those who have not" (TPJS, p. 190; 2 Ne. 9:8). This can mean that intellectual and spiritual powers are enhanced by association with the flesh. It follows that a long absence of the spirit from the body in the realm of disembodied spirits awaiting resurrection will be viewed not as a blessed condition, but instead as a bondage (D&C 45:17; 138:50). Also, "spirit and element [the spirit body and the physical body], inseparably connected, [can] receive a fulness of joy. And when separated, man cannot receive a fulness of joy" (D&C 93:33, 34). So according to this information, the child's spirit may not really have been able to progress much in the spirit world without his body.