Florence - Honeyman State Park, Thousand Trails/Encore but not sure on the non-member rentals.
http://torexatvrentals.com is just a little south of these parks. The older boys will have a blast on the quads, the younger will likely have to go on a two seater.
Also
rvparkreviews.com list a couple that are fairly good.
Little Brown Hen for breakfast. Hole-in-the-wall but good food and plenty of it, but tad spendy and cash only ATM on site. On main drag near first light north of bridge.
Champoge State Park between Salem and Portland.
Collier State Park and the free logging museum.
Lava Tubes, and Lava Lands area.