Close to the city with awesome playgrounds
The park just added two nature playgrounds that are pretty fantastic. One of the new playgrounds, right before the boat launch, features a trail with a mud kitchen, two a-frame tents and a big area where you can use fallen logs and branches to build shelters.
The other nature playground is right across from the old playground (still in use) and has a wooden water course with a hand pump and an elevated wooden plank course.
Camping can be a little loud since it's a popular spot and there are no pets allowed, but it's barely 30 minutes away from Portland and right on the Sandy River.