When we encircled Lake Erie way back in August of 1987 with our two sons (who were about the same ages as your grandchildren), one of our stops was the Henry Ford Museum/Greenfield Village in Dearborn, MI. Back then, they sold a two day pass. If they still sell this pass and you have the time, do it because it takes two days to see everything without rushing. This is a great educational opportunity for children. We camped at the KOA in Ypsilanti when we visited the area, but after all these years, I couldn't tell whether it's even still there.
We were extremely fortunate that Sunday, August 16th. While traveling on I-94 to the campground, a few hours later, a Northwest Airlines McDonnell-Douglas MD-82 crashed on that interstate killing 156 people and two on the ground (a four year old girl was the only survivor). We were totally unaware of the accident until hearing all the conversation about it while having breakfast at a Denny's the following morning; at which point, I went outside and purchased a newspaper to learn what had happened. I-94 was completely closed between the two interchanges where the crash occurred and SOP (Seat Of Pants) driving was employed (GPS wasn't available back then) to detour our way around it to Dearborn.
2009 GMC Sierra 2500HD | Crew Cab | Standard Box | 4WD | Duramax/Allison
2000 Jayco Eagle 266 | FBS | TT
1986 Coleman Laramie pop-up -- Still in the family!!!