I know that babies are supposed to lay right on the mattress and everything for a long time, but I was wondering how old before it's okay to give them a pillow? Eli is about to turn a year on Monday, when can he have a pillow in his bed? And how do you show them what it's for? Just wondering how you guys went through that, and when you gave them one, and what's good and all that. It's not a big deal, but I was curious.