OK, one of the main excursions I would recommend for the whole family would be the water parks. It is going to be hot when you are here (as you know) & water parks are great fun for everybody while staying cool. The Gypsey Beach that we have advertised is a good excursion, but last year we found that our Akyaka trip became more popular. It has a lot going on so would keep the interest of a 3 year old as well as yourselves. If you look on our website there is more information on what this
excursion involves (it is not a jeep safari). The trip to Dalyan could be another one to consider, especially if your son likes playing in the mud, but also there is some beach time & a boat trip within the day.
Hope this gives you some ideas & maybe some people who have been on excursions with their children could also recommend some excursions.