The Bible does not specifically answer this question. Will babies and children who die still be babies? Will there be children in Heaven? What about elderly people who die, do they remain elderly in Heaven?
We can only speculate where Scripture is silent. Many guess that babies are given a resurrection body (1 Corinthians 15:35-49) that is “fast-forwarded” to the “ideal age,” just as those who die at an old age are “re-wound” to the ideal age.
What is the ideal age? I do not know, again it is mere speculation. Some guess around 30, while others guess 33, since that is approximately the age Jesus was when He died and some believe the created age of Adam.
1 John 3:2 declares, “Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when He appears, we shall be like Him, for we shall see Him as He is.”