Absolutely love Portland, especially with kids. We liked:
* zoo (accessible by light rail) - go to the bat feedings!
* Rose Garden (you can do a train ride from the zoo to the Rose Garden and on a clear day you will have a gorgeous view of Mt Hood)
* children's museum, although I agree with a pp that it skews young
* Powell's
* Mt Hood. Go only on a very clear day and make sure you don't need chains for your tires. Chains are often necessary even in the summer.
* Agree with the rec to drive the Columbia Gorge. Get out and do the tour of the Bonneville Dam. Your kids will be able to see salmon swimming upstream!
* On the way to Mt Hood if you're approaching from Columba Gorge, drive the Fruit Loop and stop at farms to buy delicious fruit.
http://www.hoodriverfruitloop.com/index.html
* We enjoyed the beach and tide pools at Cannon Beach / Haystack Rock
http://www.cannon-beach.net/cbhaystack.html
And for Portland food, you must try the food trucks. They are out of this world, and there are so many to choose from.
* at 10th and Alder there are a huge number of food trucks. If you like simple authentic Thai try Nongs Khao Man Gai. The belgian waffle truck has great stuff.
* also consider PBJs Grilled in the Alphabet District
www.pbjsgrilled.com
* kid friendly very casual sit down that serves pretty healthy food: laughingplanetcafe.com