The National Geographic Trails Illustrated map of the Buffalo National River West is a great resource as it shows the river, trails, mileages, scenic spots, old homesteads, etc.
The Buffalo River Trail runs from Ponca to Pruitt and the Old River Trail follows the river. In the fall when the river is low, you can combine parts of each trail with the various access points do a number of hikes of varying length. The Trails Illustrated Buffalo National River West map is an excellent resource for planning.
I'd suggest getting the National Geographic map of the west part of the river for planning purposes.
There are lots of great trails around the Buffalo River but the age of the kids make it a bit limiting.
The Whitaker Point (aka Hawksbill Crag) trail is one of the most popular in the area and will be packed that time of year. The trail at Lost Valley is another to consider although it doesn't offer the vistas that WP does. The Goat Trail out to Big Bluff is another popular trail but it's 6 miles round trip.
The Buffalo River Trail and Old River Trail offer a lot of possibilities (starting from Ponca, Steel Creek, Kyles Landing, or Erbie. There are a number of old homesteads that aren't too difficult to get to and the hike from Kyles to Hemmed-in-Hollow isn't too difficult although it crosses the river a number of times but the river is typically very low in the upper reaches that time of year with the crossings being shallow. A good resource for trails and homesteads in the area is the Nat'l Geo. Trails Illustrated map here.
The Arkansas Grand Canyon isn't much IMO, basically just a view into an Ozark valley. I love the Ozark Cafe and have been there many times but am not familiar with the Blue Mountain. There's also a restaurant in an old gas station in Low Gap (about halfway between Ponca and Jasper) that gets good reviews.
There are fields near Ponca where the Elk gather for feeding in the mornings and evenings, always a popular spot.
Your question would get more responses in /r/Arkansas/. It depends on what part of the Buffalo you're around but there are numerous trails in the section from Ponca to Pruitt. A good planning resource is the Nat'l Geographic Trails Illustrated maps of the river. There are two, one for west half and the other for the east. The maps show the river, trails, access points, old homesteads, etc. and all the associated mileages.
When would you be going? How many miles a day do you want to hike? The Buffalo River area between Ponca and Pruitt offers what you're looking for either one-way or as a loop using the Buffalo River Trail and Old River Trail. There are also other trails and features in the area to explore. The National Geographic Trails Illustrated map of the western section of the river is a great planning tool and shows the river, trails, and scenic areas.
The upper part of the Buffalo (Ponca to Pruitt) is too low to float now. The middle and lower are low but floatable. See river conditions here.
When it's hot and the upper is low, as it is now, it can be fun to hike the Old River Trail that follows the river and crosses it numerous times with ample opportunity to get wet and swim. Get the National Geographic Trails Illustrated map of the western part of the river as it shows the river, the trails, mileages, old homesteads, and scenic spots. Link here or Buffalo Outdoor Center in Ponca may have it.
The hikes to Hemmed in Hollow, Lost Valley, and the Goat Trail to Big Bluff are great as are visits to the Villines homestead, Granny Hendersons House, and the Parker-Hickman homestead near Erbie.
Be sure to have plenty of insect repellent as the chiggers and ticks will be out.
With the limited indoor and sports activities this year because of Covid-19 the Buffalo and other outdoor venues in the state have been packed.