I'd probably pick mid October or late March/early April.

The plus for March/April, longer hours of daylight, and the rivers are more likely to have plenty of water . Minuses probably windy, maybe very windy.

I think mid-October would be perfect. We were there in early Sept this year and it was incredibly hot. In past trips, we've been there a little later, like mid-Sept and even that has been more tolerable. Since you have options, I'd strongly suggest not going in August. We don't get to travel much in Spring since our work is garden-related and those months are too busy, but I think Moab would be really nice in March/April - probably 60's daytime/30's-40's nighttime.

I would avoid August for sure.

If your boys are adventurous check out canyoneering with www.deserthighlights.com
My daughter and I have been with them twice and it is fantastic.

Be sure and see Goblin Valley State Park about an hour or so North of Moab.

You will probably want to avoid the Jeep Week in Moausually in April I think).

Jeep Week always ends on Easter Sunday, so in 2013 it runs March 23-31.

If you can go early April, that's a great time. But late March would be super busy in Moab.

Thanks for the replies. I was guessing that August would be too hot but it works great due to summer vacation. Maybe we will go to Jackson Hole then. I will explore the October time frame during their Fall Break. Their Spring Break seems to coincide with Jeep Week. Thanks for the heads up there.

Taitai

I really like the Pacific NW during August. Maybe Seattle/Mount Rainier/Whale Watching at San Juan Islands

Or Oregon/Crater Lake.

Yellowstone, Tetons, and Jackson will be super busy in August.

See August is my favorite time for the kids. We can spend all kinds of time in the water and they don't get chilled like spring and October.
Our family likes to raft, stand up paddle board, canyoneer through potholes. The long day light hours tire them out, me too. we do our hiking after dinner and do shorter routes. The Moab Library has had Cardboard Boat races on Ken's Lake which can be a load of fun, if you know about it to come prepared to compete. ANd YES it works beautifully with summer break.