@Harold - next time you visit the Roman Baths, the kids audio guide is accessible from the regular audio set. You just have to punch in the numbers which are given at each location. Last visit I had plenty of time so I listened to the regular narration, the kids narration and the one by Bill Bryson, lol! So interesting! I suspect since OP is on a coach tour they will just have time to do one of their choosing.
I had time this morning to look around the website for the Roman Baths. I see they now have a separate children's app can be downloaded as well. I'd download what you can before you travel and make sure everyone has their earphones with them. It doesn't look like the regular adult audioguide is available on an app yet. What I thought was a link was just a link to a googletranslate app.
https://www.romanbaths.co.uk/childrens-app
Checked the official Stonehenge site and yes, it now offers an app for it's audio guide.
https://www.english-heritage.org.uk/visit/places/stonehenge/plan-your-visit/stonehenge-audio-guides/
Last visit (2018) the only place that had a downloadable app for their free audioguide was Westminster Abbey and that worked so well. First, your phone is way lighter than the heavy duty audio guides. Second, who wants to put that thing up to your face when thousands of others have too? Yes, they clean them but still...yuck.
So...check for the locations you are visiting to see if you can download an app ahead of your travel!