Zion Np/ Moab / Grand Canyon North Rim

Well you want scenic and adventurous Zion- virgin river narrows, yes there will be a million people but the farther you walk up the river the less crowded it gets. You could also do the Subway at Zion it requires a permit. The 5 yr old would be very questionable on that. Angles landing as someone mentioned the lookout would be the place to have the 5yr old and someone else remain behind. No way would I let my 5 yr old do the last bit.

Leave the NR GC and head to Page and do the upper and lower Antelope Canyons short hikes extremely scenic slot canyons. If do some net surfing you will easily find pictures. You do not need to hire a guide service/tour company. The Navajo Nation does charge to get in and it isn't the cheapest hike you will ever take for sure even without a guide which again you do not need one. Another good one there and cheaper is Water Holes Canyon either above or below the highway or both.

Once out of Page Navajo National Monument
Monument Valley
then you can hit Cedar Mesa off hwy 261 not sure what you are driving but the Moki Dugway may impede your ability to get up the road as it has restrictions but there are fantastic indian ruin hikes up there way to many to list. Fallen Roof Ruin would be one you can google.
Valley of the Gods road,
Goosenecks of the San Juan.
Canyonlands Needles District has hiking galore would suggest Chesler Park, Arches as mentioned Fiery Furnace, Delicate Arch and Devils Garden add in the primitive loop the loop may be more than a 5yr old can do though.
Canyonlands Island in the Sky District mesa arch among others
Dead Horse Point
Northeast of Moab on HWY 128 there are several hikes along that road Negro Bill, Onion Creek fisher towers etc off Potash road a few more Corona Arch, Culvert/Dragonfly

There is lots of hiking at all of these parks.
Zion, maybe take a horseback ride through the park. I think you can book them inside the park.

Moab is large enough that you can do pretty much any activity you want to.
I recommend,
Renting a jeep and taking a 4WD tour.
Rent some mountain bikes, this is, after all one of the most popular mountain biking areas in the country.
Take a raft trip.
Take a plane ride.
Jump out of a plane, with parachute of course:)
Take a dinner cruise on the river.

Zion NP:

One of our favorite hikes at Zion is the one that starts at the east end of the tunnel called Canyon Overlook. Finding parking is harder than the hike. Very doable for the five year old with a lot of cool (literally) places along the way. Short hike but with an outstanding view of the Canyon from a different angle.

Yes, the hike is very interesting and very easy with grand reward at the end.

Since it will be HOT, walk up the slot in the river as far as you like if the water level is down enough which shouldn't be a problem this late.

Another nice hike with a cool reward at the end is the Emerald Pools Trail. Can be a bit busy since it is right across from the Lodge.

If you have bikes, take them on the shuttle to the end of the loop road. From there, it is mostly a down hill coast. There is one short steep hill that is easy to walk back up and then down hill again to the main road. Last 1/2 mile back to the campground is flat. The shuttles carry only two bikes so send an adult and the youngest on the first, the two older kids on the next, and the last adult on the third. The driver will watch out for two oldest and they will get a kick out of being trusted to ride the bus alone. When we did the bike ride, there was only my two daughters aged 14 and 12 so I sent them up first and came up second.

For Moab check out the jet boat ride on the river.

If you want to go up to Angel's Landing, the five year old could stay back at Scout's Lookout with one of the adults. Depending upon their experience, maybe even have the 9 year old stay back. That last portion is very, very steep. Still a great hike through the Walter's Wiggles portion of the hike even without going the last bit to the Landing.

One of our favorite hikes at Zion is the one that starts at the east end of the tunnel called Canyon Overlook. Finding parking is harder than the hike. Very doable for the five year old with a lot of cool (literally) places along the way. Short hike but with an outstanding view of the Canyon from a different angle.

Just be aware that there are steep drop off throughout the park that are not fenced and may be unstable.

Also if you are coming from the flat land of the midwest be sure to watch out for signs that the elevation is bothering the kids or the adults while at the North Rim of the Canyon. It can feel like flu or stomach aches. Bring and drink plenty of water.

How much time do you have?

Your location says Detroit, are you flying out to Vegas first and renting a camper, or something else?

From Zion to Moab there are so many sights to see. Bryce, Kodachrome, the Hogback, Capitol Reef, Valley of the Gods / Natural Bridges, etc etc.

We just got back from Bryce, Zion and Moab.... It's HOT!!
Angels Landing maybe too much for a kid that young. You could not take your hands off them in the narrowest section. In Moab go to Arches and hike Devils Garden and the short hike to Delicate Arch. There are also many great hikes outside of Arches like the hike to Corona arch, just Google it.
Have fun, but if it doesn't cool off you will be pretty miserable. You can also do the Narrows hike in the water in Zion to cool off, just be prepared for a million people.