J.W.
My best advice is to get him outdoors as much as possible. Little children are building and developing their physical and mental abilities and running in a park where there is plenty of room to run and things to discover is a great way to do both without feeling like you stuck with a caged bird. Also there are several studies that show that lung development, healthy attitudes about physical exercise, and the immune system depend heavily on outdoor activity. Also it is good for the mood. Even an hour a day you will see improvements in concentration and less pent up frustration. This is the perfect time to get out there. Even if it is just walking in your neighborhood, but here in DFW there are plenty of awesome parks and nature preserves.
PS There is some fantastic studies you can find by researching outdoor preschools which are very popular in Europe and are now spreading here. Here is one such place
they have some great articles.
http://secretgardenoutdoor-nursery.co.uk/