How do you know it is time to lower the mattress on your crib? When you go in to get your baby out of bed in the morning and find him looking back at you like this. By the way he is doing great with tummy time. I added these two other picutres I took yesterday. We have to get a couple rugs because our apartment has only tile and wood floors now that he is starting to move around he needs to have the space to do that and I don't want to put his bare knees on the hard floors not to mention him bumping his head on them. Right now he is on the ottoman with one of us right next to him. He is really holding his head up well now.