DH, DD (11m) and I are heading to Portland, OR next month. We like cool stuff. I drink tea, DH drinks coffee, DD tries to steal our mugs. We hike. I take pictures. DD likes trees, dogs, and leaves.
We have a good idea of what to do outside the city, but what about in the city proper?
For hiking, Forest Park is right along the edge of the city but you feel like you aren't in the city. You could also drive out to Cannon Beach and do some hiking at Ecola State Park. We did all of that without our daughter but if you wear her in a carrier, I think it would be fine.
the childrens museum and zoo are fun I like to go to the farmers market at PSU on saturdays (it's different than saturday market which people love but I like the farmers market better) walk on the waterfront NW 23rd- shops, Salt and Straw icecream... near soccer stadium there are a lot of kid friendly bands that play on different nights or mornings at coffee shops (PDX kids calendar has the details). Mississippi Pizza has kid bands a few times a week.
We visited friends out there a few years ago. We don't have kids but some of the things we enjoyed were people watching at waterfront park (downtown area), eating at the food trucks, and the museum of science and industry. We were there in the spring and also enjoyed driving around looking at the pretty views. The rhododendrons were in season then and it was gorgeous. I would love to go back.