I've done several things on different trips to keep track of location.
Low-tech: Write it down on paper (the time table on a train trip, or a map on a road trip). This is really easy if you set the clock on the camera accurately and keep track of when you are at stops. Add a lesson about time zones and decide how you are going to handle them (on camera and in notes).
Semi-tech: Take photo of gps screen or gps app on phone right after taking scenery shots. Take photos of signs that tell location such as depot signs or businesses that have location as part of their name.
Hi-tech: Run a phone app that makes a track of location every few seconds, then run that file and photos through a program that matches the times and adds longitude and latitude to photo metadata.
Alternative viewpoint: Don't worry about where the photo was taken. When I look at photos from when I was a kid, I'm more interested in when (what year) than where. "Our first train trip" is probably good enough.
You might get better buy-in from your kids if you discuss all this in advance and see what they want to do.
This also ties in with your other questions about entertaining them. I think cameras are a great way to keep them interested and occupied but they should understand when and where photos are not polite (although legal). I also think they'd learn and see more if photos are rationed somehow. I've traveled with a couple of adults who look at the world through a lens for lengthy periods and they really do miss out on a lot.