x3 on Itasca State Park, one of our favorites in the whole country. Keep in mind that it's a good 3 1/2 hours from Minneapolis. Another not too well known recommendation that an 11 year old might like is the Soudan Underground Mine State park, also pretty far north. They have an awesome tour of Minnesota's first iron ore mine, 1/2 mile underground, as well as a tour of the high energy physics lab that was built a few years ago in one of the big caverns. They use the lab as a target for particles shot from the accelerator in Fermi Lab outside of Chicago, 400 miles through solid rock. Way cool stuff. If you start in Minneapolis, you could do a loop up to Itasca, across to Soudan, and then continue to the North Shore (check Gooseberry Falls S.P.), then back down through Duluth and maybe pick up the Great River Road as you head back south. Hey, I want to go! Too bad I'm out of vacation for the year.
Soudan Mine brochure