AJ has been rolling onto her side for about 2 months. I don't know how many times we have stalked her with the camcorder, sure that she will finally "go all the way" onto her belly. She's come really close in the past few weeks, but each attempt ended with a loud "fwump" as she flopped back over onto her back again. As she gets more adept at interacting with her environment, however, she's started to experiment with aids to rolling. She particularly likes sticking her feet in between her crib slats, and discovered that she can use them to stay on her side. (Sometimes she even puts herself to sleep that way which is quite funny.)
Well, today AJ finally made it all the way onto her tummy! I missed some of the action because she was in her crib and I was washing my hands. When I got back she was already on her tummy, parallel to the short side of her crib. She was lying on her right hand which she was working out from underneath herself. Once she was fully on her tummy, she was calm enough but a bit at a loss of what to do (as usual). I congratulated her and left her there for a while. She lifted her head and looked around, attempted to push up with her arms a little, but didn't make it very far. She was calmer than when we put her on her tummy (she despises that). Eventually she did start her frustrated cry however so I picked her up.
Most of AJ's milestones are gradual, so it's hard to put a date on them. And I suppose this one is too, because she's been doing the partial rolls for so long. I think she could have managed the roll last week, because again I walked in on her and she was up against the far side of her crib, almost face down. But it was such a weird position for her to be in I involuntarily exclaimed "What the !@#$ are you doing?!" and she immediately rolled onto her back to stare at me. But it is fun to witness her reach this milestone. We'll see if she keeps rolling now, or if she decides "Meh, that wasn't all I thought it would be."
I do see now why it is so important to have a fitted mattress, and not to use bumper pads, because it would be easy for her to get entangled in it.