S.T.
Cook Park is a good option in the Tigard area. It's not too far from the Carman Drive exit on I-5. There's lots of trails along the Tualatin river and at least two playgrounds. Trails are now connected to Tualatin where there are more playgrounds or you can go into town to the shopping areas where you can stop for a coffee. Let me know if you want more clear directions as I live in the area.
Parts of Tryon park near Lewis & Clark college are also paved and nice for walking.
S.