L.K.
If he is not fat, he may just need the extra calories to sustain his growth. Generally at 6 yrs old they eat according to what their bodies tell them that they need. Just make sure that you have lots of healthy choices for him to eat, and make sure he is playing (with you, or a friend) so that he's not eating out of boredom. My six year old in Las Vegas has friends come over. Even though it's hot, they do play out side for short 10-20 minute spells. I just make sure they have lots of water outside with them.