Las Vegas usually has cheap flights. And it's close enough to do the Grand Canyon or Utah.

There are several campsites along the Outer Banks. It’s very kid friendly, but not too touristy.

I'd do a search and see if anything isn't going on due to covid, but from what I've heard you're probably in the clear in FL lol

Treasure island is my fav! Anna Maria is also amazing but can be hard to find parking on busy days if you’re not staying right there. If you go to st Pete or treasure island, downtown st Pete is super close and very cute. There are lots of restaurants there

I’d be well rested before you cross St Louis because there is nothing to see or do past there. And hardly any places to stop.

Go do the Van Gogh immersion exhibit in St Petes A treat. Paddle boats etc...in downtown.

Probably not a popular answer but I adore beach haven NJ. It has a little of everything and if you stay in beach haven itself you can pretty much walk everywhere, which might be nice with special needs. They have a mini amusement park and arcade, an old school ice cream parlor, a theater with kids shows and regular plays, lots of relaxed places to eat.

Clearwater! And if it’s too packed Indian rocks Beach is just down the coast