If they get to Detroit, the Henry Ford Museum is outstanding. I have been there three times and have enjoyed it immensely. Depending on time available in the schedule, you could spend two days in the museum. Also, next door is Greenfield Village, where you can easily spend a full day or longer. I'm not sure if they still have the Ford F150 truck assembly plant tours or not, but again it is something special to see.
https://www.thehenryford.org/
The two museums in Auburn Indiana are also a not to miss visit.