We just started putting DD in her crib this week (she's almost 11 weeks old) and I did remember to remove her bumpers that came with the bedding and put in her breathable bumper. Good thing I did because when I put her down she was laying in the middle of the crib (in her sleep positioner) with her head and feet facing the short ends of the crib. When I checked on her the next morning she had somehow moved where her head was up against the long end of the crib, basically going from horizontal to vertical. I'm so glad I took out the bumpers! She probably would have been ok but it would have panicked me.
By the way, I have no idea how she moved that much - she also started turning on her aquarium with her head so we put her feet next to it - hope she won't wake herself up by kicking it on
Re: F/U to crib bumper post