T.K.
Nash Farms in Grapevine is fun. You could do a day trip to the farm and per the animals and climb all over the tractors.
You could go camping at Cedar Hill State Park and teach him to fish. All little boys like camping. Then have a birthday bbq at the lake. Extended family could just pay the day pass to get in for the bbq.
There is an indoor play place in Grand Prairie called Abbeys Plalyhouse. They do parties. There's a jump up place in S Arlington off Cooper and Sublet that does parties. It's a giant bounce house full of inflated bounce houses and slides.
Ellens Amusements in Cedar Hill, I think it''s off 1382 maybe, is crazy cheap. Go carts, batting cages, putt putt, video games. My 3 and 4 yr old loved riding inthe go karts with us. You can find coupons online.