Bend would be fun-
You could stay in Sunriver- lots of bike paths, etc. Sunriver also has outdoor pools, canoeing, horseback riding, all kinds of family friend activities. Check them out- they have houses you can rent too, if you are looking to eat in more.

Bend has Lava Caves, The High Desert Museum is really fun (we took our DD who was 3.5 at the time last summer- she had a blast!) Go to the top of Pilot Butte in downtown Bend for a great view of the mountains. If it is off season, you could ride the chairlift to the top of Bachelor!

Have fun!

I agree with PP- tripadvisor forum would be a great option to check out!