July will be hot and humid. Your family should try and find a water activity. If your on a budget like I am Destin commons (a shopping center) has a play ground with a water area. There is always the beach but if the waves are too big for the little one. OkaloosaIsland has 2 beach access points on the bay side. One you can’t miss it’s on the north side of 98. the other one is tucked away behind the convention center.
West of Okaloosa Island over Brooks brige there is a park south of 98 no water area but it has some big trees that keep it cool
Further west in Navarre there is a water park just west of the bridge.
I also agree with the naval air museum “Great place” but it is 1 ½ hour drive from Destin there is an air force armament museum it’s a lot smaller and most of the aircraft are out side but it is only 30 min drive.