Oregon Zoo - This zoo is large and will take up the whole day if you like. It is a beautiful zoo and plenty of places for a picnic so pack a lunch. For more info click here.
OMSI - This has an awesome area for younger kids as well as lots of displays for older kids. We really enjoy the kids areas and the science experiment areas! The ball room is also lots of fun. You can take a picnic here as well. For more info click here.
Multnomah Falls - I would suggest getting on Historical Columbia Highway in Troutdale, OR and taking that up to Crown Point and then hitting one waterfall after other. I believe they start with Latourell Falls which is extremely easy to get to. Just a short walk. The next it Bridal Veil which is a short hike but is steep. There are about five water falls that are very easy to get to if you just keeping going down the road. The last one is Horsetail falls. For more info click here.
Saturday Market - Vendors sell all kinds of things here. We always had fun just walking around and looking at stuff. For more info click here.
Farmers Markets - There are farmer markets all over the place. There is one in downtown Portland on Saturdays. Click here for info on that one. They also have them in every little suburb around Portland as well. Click here to find some of the others ones around the area.
Blue Lake Park - This easily became one of my favorite places. You have to pay around $4 a car to get in. There is a beach area with a roped off area for the kids to swim in. There is a splash park, biking trails and more. For more info click here
Jamison Square Park - Such a great spot when it is warm. There is a water area where kids can play. The water builds up and then drains before it gets to deep. Which means as a parent you can actually relaxing and not have to worry as much! For more info click here.