Bug/Issue First child wont grow past third stage.

My first child has been in the third stage of his life for a while now, and during that stage my spouse asked if I would like to have a second child. I agreed, and she's been born already- but my son is still in his third stage of life. This doesn't cause any problems, but it's a little strange watching my children merge at night when they're both asleep in the same crib. He should have become a toddler and started sleeping in the bed at night, shouldn't he? It's been well past 14 days, which I read was how long it took for them to grow. I assume something bugged out but, I'm not sure what?