Portland is the largest city in Oregon with the largest airport in Oregon. It's seen here (barely) with Mount Hood in the background. We spent almost a week in Portland without ever a glimpse of Mt. Hood. When we returned at the end of our trip we had several clear days with good views of it. There's a lot to do in Portland, a lot of good restaurants and a lot of interesting neighborhoods. The distributed nature of the city means that you're likely to be traveling back and forth across it however, and if there's one thing we didn't like about Portland, it was the traffic. There is extensive public transport but it doesn't often seem to go directly from where you are to where you want to be - at least for us it didn't.
This is the International Rose Garden, on a hill just west of the city center. One of Portland's seemingly endless nicknames is 'the Rose City'. If you're visiting with kids, you'll almost certainly end up somewhere up on this hillside which also holds the Children's Museum, Washington Park and the Portland Zoo.
Speaking of the Portland Zoo -- it is quite large. We spent the majority of a day here. The zoo is also directly accessible from the MAX lines (public transit).
We only spent a couple of hours in Salem, mostly centered around the state capitol complex. It was a weekend so things were extremely quiet in town.
The park around the state house is quite nice. There are some assorted very large trees, quirky sculptures and a useful plaza full of all the state flags. At least, it's useful if your child is currently obsessed with state flags.
The next city down from Salem is Corvallis which we completely ignored on this trip. Sorry Corvallis. Instead we jumped straight to Eugene, home to the University of Oregon. Eugene seemed like a really nice town to us. There is a lot of green space along the river and one of the more interesting city parks we've been to (Skinner Butte). We found Eugene to be quite a bit livelier than Salem (at least on a Saturday in the summer).
Eugene also has some large public rose gardens. So did Salem for that matter. We would like to also mention that there are a lot of vineyards in the Willamette Valley. We'd also like to offer personal recommendations and stories about visiting them, but with an assortment of small children in our party, we didn't actually visit any. Alas.