K.W.
The Orlando Science Center is awesome--and in our many months of hot weather a great place to take kids. They have great exhibits and an IMAX theater.
http://www.osc.org/
Right next to the Science Center is the Art Museum. Your son may be a little young to enjoy it, but they have some great exhibits and offer camps (as does the science center) in the summer.
Orange and Seminole County have some awesome parks too. As do the cities of Orlando and Winter Park. You can find the ones close to you and their facilities by going to each of the
city or counties respective site. For example for Orange county go to
http://www.orangecountyfl.net/dept/cesrvcs/parks/?REDID={...
But this will only have the county parks and not Orlando, Winter Park, Altamonte Springs, etc city parks listed.
Orange County has some that have skateboarding ramps and half pipes, disc golf (aka frisbee golf), splash parks, lakes, etc. plus the usual playground equipment.
The YMCA is also very big here in central Florida with tons of resources for families. Their membership is well worth the many things they have to offer. (but you can still sign up for sports, camps, etc without being a member). There are Y's all over too so I'm sure there is one relatively close to where you live.
Oh and when you get a chance, take him out to Merritt Island where the Space Center is. They have LOTS of stuff to do and kids love it!
There are summer camps for EVERYTHING around here--so whatever yours sons interest you can find something. Anything from the usual YMCA to Sea World, Arts, sports, Drama, etc.
Another great site to find things like that is
http://gocitykids.parentsconnect.com/?area=176
Hope that helps and welcome to Orlando!