There might be a delay until they show up in the trade centre.
Just tonight I had two baby elephants (age 0.0 years) pop up in my trade centre. In one case I actually saw it appear in there while I was looking through the stored elephants to decide which ones to put into a habitat that I had emptied a couple of minutes earlier for this week's challenge.
And here is the kicker: going by the list of siblings (the parents were "unknown") that little baby elephant belonged to the parents I had released to the wild and must have been born years before it appeared in my trade centre. The other elephant also belonged to parents I had previously released, but since I did not witness when it showed up in storage I can not say if there was a delay, too.
So, if this is the same bug your baby elephants might still be on their way to the trade centre on paths unknown to man (i.e. the server somehow holds them hostage for some time or something like that).