Most areas have some sort of historic areas that you can take your family to for free. It may be a memorial, an Old Town section, old homes, etc.
Take advantage of these and teach your kids a bit about the history of the area they live in. It’s a bit more immediate than what they learn most of the time in school, and that makes it more interesting. And have fun doing it!
This is a great idea! We’ve done this before, but it’s one of those things that is easy to forget about. In the past, we’ve taken our kids to an historic railroad station (costs to ride the train, but it’s free to watch it go), walked around the historic sections of Philadelphia, and on vacation we did a self-guided walking tour of Savannah, GA. We’ve also done tours of 2 local chocolate factories and a pretzel manufacturer.
The kids love the opportunity to see things first-hand, and you might be surprised what could pass as a “field trip” to a child — we spent an hour watching bulldozers work near a hospital once.