I can't recall if there were goals attached to the babies or not but so long as the craft isn't greyed out and you can click the question mark in the lower right corner to read the animals description, you should be able to craft the baby. In the case of the Flygers Cubs and Wyvern Hatchlings; you can only craft them if you have the grown versions as pets because they're the only ones that drop the milk needed in the craft.
There is a section of the HUB about Ivy's Nursery with the relevant info and links on the subject that may answer any other questions you have:https://forums.storm8.com/showthread...-Magic-Nursery