Every baby book I've read on the topic of sleeping has enforced one common principle - follow a nightly routine. Our nightly routine consists of the following: dinner, jumperoo, bath and then most importantly NAKED TIME! Naked time means letting Charlie play for a half hour or so completely sans clothing and boy does he love it! When Charlie is naked he squels and shrieks with utter glee! Hopefully he will grow out of this phase when it's not so cute anymore! But for now - we'll keep it part of the routine!
Look at those little butt cheeks!