How old is your son? When I lived down on the Gulf Coast of Mississippi, with 3 kids...NO a/c....We would do anything we could think of to stay cool. One fun thing was fill up a kiddie pool with water, pour in some baby shampoo....gotta have the bubbles....and let them have at it.
Or, squirt guns. The baby would like the bubbles, that you blow. Add some watermelon chunks to slurp ....they can wash up in the kiddie pool. After that, we would either have a very late supper....9 pm....and then they would happily go to sleep.
I would also spray down the bed sheets with cold water mist.