By the way, I don't think colonists should be able to breed. Kinda ruins the point of population limit of story tellers and such.
Unless you can make it rare, and make the female parent lose the ability to do work for 14 game days while the child stays with her (Maybe even disable the male from working for 2 game days), you need a child sized bed too for the child and only children can use. Then for 30 game days, the child will be in teen state, using same child bed though. In teen state, he can do only certain kinds of work such as hauling and cleaning, cooking, growing, then when adult he gets his traits, childhood/adulthoods, and such. Though you need custom childhood/adulthood for this and always set the colonist age to 15. I guess you could use settler as the childhood and adulthood states though.