Hi!
Will be in Paris Oct 9 - 14 with two young children. We've been to Paris 5+ times previously and are staying 5 nights in the 7th. Wanted to have one base for the 5 nights to avoid lugging kids and kid's stuff from place to place but would love to take at least one day trip while there (possibly two?!). We've previously done Giverny, Versailles, Normandy, Loire ... open to any suggestions! Been two years since we've been in Paris ...
You might consider Chantilly, especially if your kids like horses.
Provins? Medieval village with a fort. Depends on the age of your children.
Strasbourg
OK, with kids, you need to consider the Parc Asterix. Asterix is a series of comic books about a Gaulic warrior who fights the Romans. There is an amusement park near Paris.
https://www.parcasterix.fr/en/prices-and-ticket-office
Don't go to Disneyland Paris - so USA-centric. Do something French. You can start off your kids with some of the comic books.
I have not been to Parc Asterix, but I think a European amusement park would be a great memory for your family. Our daughter's first amusement park, when she was 4, was Plopsaland in Belgium, and it was a lot cheaper than visiting the Mouse.
In which direction from Paris?
I did a number of places from Paris this time as day trips or afternoon trips....Albert/Somme, Soissons, Rouen, Troyes, Maubeuge, Bar-le-Duc, Orleans, St. Quentin,