While vacationing in Northern Arizona last April, we took a jeep tour in Sedona. Our driver mentioned that northern Arizona never gets as hot as southern Arizona because it is at a much higher altitude. According to him, only a few days each summer reach the 90ies and it has never gone over 100 degrees in Sedona. However, we need to emphasize that we have never visited Sedona in the summer, so we can't guarantee this information is correct.
Will your children be happy? It depends. The red rocks of Sedona are incredible, but I doubt beautiful sites will keep children happy very long. I also doubt they will be interested in the vortexes or the numerous art galleries in the area. They might like a jeep ride into the surrounding countryside, but it is expensive. It is also extraordinarily rough (almost to the point of whiplash, if our tour was typical). If you decide to go off-road, we strongly suggest a professional tour because we passed several broken cars that tried to do it on their own.
Arizona has many places that might interest your children.
If your kids like zoos, they will love Out of Africa, a wildlife part that is easy driving distance from Sedona. They have a great tiger show (despite the fact there are no tigers in Africa).
Montezuma Castle is also nearby, but we didn't have time to visit, so we don't know if children would like it.
Driving through the Oak Creek Canyon should also impress them with its steep walls rising on both sides.
The Grand Canyon is driving distance from Sedona. We stayed in Flagstaff, so we're better at distances from there, but it will probably take you around two hours to get there, much of it on a two lane highway. There are a few interesting places along the way (for example, you can pay to see white bison that are sacred to Native Americans).
We estimate the Painted Desert and Petrified Forest is about 1 1/2 hours from Sedona, and you stop at Meteor Crater along the way.
Lowell Observatory, which is located in Flagstaff about 45 minutes north of Sedona, is great to visit at night because they let you look through their telescopes. A friend told us we can look at the sun through a special telescope during the day, but it wasn't offered the day we visited. Lowell also has shows and interactive displays. If you visit at night, we suggest you take the highway back because the road through Oak Creek Canyon might be difficult in the dark.
Our friend also recommended Sunset Crater, which is north of Flagstaff, but we didn't visit. There is also another canyon (I don't remember the name), but it was closed when we were there due to a landslide.
The same friend also drove to Phoenix to attend a baseball game. However, Phoenix will be very hot in the summer.
I hope this helps.
Donna and George