With the first baby, my daughter fed it, changed it, cuddled it etc, so the needs were all full. I'm going to go get on the game now, so I will see if the option is back, and I'll try putting the aging on if it's not.
I'm just worried that my daughter (who is 9) will end up neglecting it if it stays a baby, and social workers will take it away and then she'll be devastated. In Sims 3 on console, she accidentally drowned her child daughter, she made her swim while fatigued, and she didn't have the energy to climb out of the pool. She burst into tears (granted, she was younger then), and of course her two brothers laughed at her, which made it worse.