S.W.
I have the same thing with my 4 year old. He sweats a lot in general, esp. when he is playing outside. Sometimes I pick him up from daycare, and it looks like he just came out of the shower. His head is also very sweaty at night. It seems to be in the beginning when he falls asleep, then after a while, it seems to go away. I have a 2 year old who does not sweat at all, so I don't think it's anything to worry about. I did mention it to my pediatrician and he did not seem concerned.