Here is something I posted on another thread previously with some comments in parentheses, but it is all mostly still true:
Rafting the river is a great way to cool off one day. (Might be a bit cool for it this time of year though) It is pretty low key rafting. We used Moab Adventure Center for a 1/2 day trip in 2021 and enjoyed it. You can ride in the big raft with the guide or you can do 2 person inflatable kayaks paddling along with the raft. We did the kayak and had several folks jealous when they realized they could have had that option. Sitting on the side of the raft without back support is apparently only comfortable for a while. Much easier to lean back and rest in the kayak. Even with a half day trip, they start a little later in the morning and they feed you a lunch along the way.
As far as what to see or do, Arches and Canyonlands are the two obvious draws as far as NPs go. Check online because I think Arches has gone to an entry permit system (they have, but maybe only for the summer months). If it is hot, plan to get into the park right after sunrise if you want to find parking at the popular trailheads. Delicate Arch is an iconic location to hike to, but if the kids aren't up to a moderately strenuous walk, there is a much shorter overlook that will get you a view of the arch without having to hike all the way up to it. One of our favorite things we did in Arches was to grab dinner and then head into the park at sunset and do some twilight hiking and stargazing around the North Window/South Window/Double Arch area. If you like doing long exposure photography you can get some great shots of the arches with a partial moon in the sky. The Devils Garden and Landscape Arch trail was a nice easy hike and gets you right up close to several arches. Whatever you do hiking around there, take lots of water.
In Canyonlands, I would recommend the Islands in the Sky (northern portion) of the park over the Needles (southern) section. Upheaval Dome is a really cool hike and gives you a great view of the Green River Valley to the west. If you hike up to the rim of the dome, keep going around to the west (left) and you eventually reach an area with a really great view of the Green River to th west. The White Rim Overlook trail is a cool hike in late afternoon when the setting sun starts throwing shadows across the canyon floor. The Grandview Point trail is another short but good one that give an incredible view of the confluence of the Colorado and Green Rivers in the valley below.
Keep in mind that many of the restaurants in Moab close down fairly early in the evening (This was in 2021, when they had a hard time getting staff coming out of Covid, so may not be as true anymore), so your options may be limited if you are coming back into town late. Plan ahead for where your meals are coming from on those days. We really enjoyed the Moab Diner (try the sweetwater potatoes and the ice cream). Moab Brewery was reasonably good food too. Antica Forma is good pizza and easy to pickup and take into the park for an evening meal. The Quesadilla Mobilla food truck was pretty good too.