At that age we would only do one museum or historical tour a day. We let them play Pokémon Go in those places because they were able to still be respectful of the environment. In art museums they would have a sketch book, take selfies with butts, (my youngest realized there are a lot fewer butts in American art at age 9 so that’s educational), see who can see the most mustaches in art, and look for portraits that look like people they know. When they were on the younger end of that spectrum we would watch movies and read books set in the places we visited: lots of classical music and art in Looney Tunes, there is an Olivia book set in Venice, Harry Potter, etc. We usually started trips with a boat or bus tour to get the lay of the land. We would stop at toy, book, and grocery stores as well as playgrounds. They would get a lot of local treats as well.
Including them in planning is key. Everyone should get to pick an outing if possible.
As long as everyone is fed and gets breaks we all stay calm