Definitely the best move re OKC. If they're going with a hotel, I know the Hilton Garden Inn and the Homewood are both owned by Raymond Management. They're a former client that owns/operates hotels in that mid-market range and do a really nice job with their properties. The bricktown Renaissance is really nice too.
In terms of activities, the Riversport Adventure Park is walkable. It has a huge ropes course, tons of bike trails, and I think a zipline that crosses the river. If the weather stays decent, the whitewater center is right there as well. It's where all of the 2028 LA Olympic whitewater events will be held. I think Dude Perfect has done some videos there as well. Check their website to see about reservations for rafting or tubing availability. Reserve early if that's something you're wanting to do.
There's a big rock climbing gym nearby, a bass pro (yeah, yeah), movie theater, mini golf, and plenty of places to eat. On the west side of the RR tracks, there's the botanical gardens. There's some activities there. Also a seasonal ice rink (though its pricey and usually sucks because its just too warm and slushy). A few blocks south is scissortail park. It's a relatively new huge outdoor green space for whatever activities you feel like.
OKC has exactly one skyscraper (not really true, the skyline just looks that way from far off). I think you can go up to the top. If not, there is a restaurant on the top floor. Pricey but good; views are fantastic.
If you like basketball, the Paycom center is right there. Thunder games are pretty fun (but I'm spoiled on this one. My inlaws are friends with one of the seven guys that own the team so we usually have free floor seats when we go).
Go see the Murrah building memorial. It's probably pretty heavy for 12-13 year olds but its well done and quite moving.
Oh, and go check out the American Banjo Museum. Surprisingly cool.
