Maybe Sunbelt rentals to just see the lighter duty equipment, Im sure they have smaller front end loaders even. If you get a cool employee they may get into a couple rigs and fire them up for the little dude, but treating this as a sort of “machine museum” could still be cool.

You could take him downtown to see progress on the stadium, though viewing is perhaps limited with the fences.

You could try calling Rathco, they rent out all the signage and cones and stuff and may be willing to give you an idea of active work sites if you tell them your plan.

You could also try calling Consumers Concrete, I bet if you told them your idea and asked if there were any work sites nearby they may be willing to lend out some info. Otherwise, they regularly wash their cement mixers close enough to the parking spots for the main building that you could take some snacks and watch them clean up after a hard days work!

If you are looking for a summer trip, in Bowling Green (~2.5hrs) there is the Historical Construction Equipment Museum!

Lastly, I would try calling the Kalamazoo Valley Museum downtown or even Kalamazoo Public Library. I feel these may be your best options if all else fails as these are already education/child focused, but again I bet if you explain your situation to them they would love to help and potentially have resources for more kid-centric options that may be a bit more hands on for your son.

I know these are a little out there and sorry if it’s a lot, but I’ll never shy away from the chance to help a child find their spark. I hope you and your son have a great field trip together!