Spoiler included
Actually, unusually short childhoods are really nothing new. Anyone who watches soap operas will tell you that children frequently age very rapidly, sometimes as many as 15 years in just 9 months. It has also been noted that many soap characters seem to hang out in their late 30s for as long as 20 years.
It is my theory that they are banking away their childhood in exchange for more time in their prime, all through the miricle of compound interest.
It could well be that something similar is happening in Dragonlance, in this case, using the banked or possibly stolen time to prolong the prime plot lifetime of prominant characters.
Only Time Will Tell...
Spoiler space follows.
For what it is worth, having read the novels in question, it is worth noting that most of the new elves are indeed not pure elven, and the only 'child of the heros' who was of questionable age was born 'off-screen' at a not precisely placed time, and conveniently died at the end of the trillogy.
And no, I have never watched soap operas. Not once. Uh-Uh. *Shakes head emphatically*