Check out castelnaud.com. They have tours of the castle and reenactments, plus catapult demonstrations. Your kids should enjoy it, plus there are supposed to be beautiful views of the valley. We will be there in June with kids and grandkids (9 and 12). Being there in July, you will find many more family-oriented activities at many of the sights. Lascaux IV has interactive displays, etc. We will go there, plus Font de Gaume. Per this forum, that is the primo cave to visit as it is the original one that you get to explore.
We hope to go to a marche nocturne (night market) on a Thursday at Sarlat. The night markets are supposed to be like parties, with food and drinks and music. In July and August several villages and towns have them on different evenings, but we could only find one in June, in Sarlat. Check out jours-de-marche.fr/24-dordogne for details about all the markets and night markets. It is a great resource recommended by another forum member.
We also want to visit Beynac Castle, another highly recommended one. Between castles, kayaking, beautiful villages, markets, prehistoric caves, gardens and relaxing at the pool at our gite, the kids and grandkids should have a great time! They may use the bikes provided for exploring the area. Oh yes, there is a tour of a walnut processing business. I don't know much about it, but it is in Sarlat and sounds like a fun, brief interlude. Don't forget wineries and goose farms to visit.
By the way, Rocomadour, St. Cirque LaPopie and Peche Merle are in the opposite direction from Sarlat as Les Eyzies and Lascaux, so you might want to consult a map and group your places to visit somewhat together to avoid doubling back. Distances are short, but the roads are too small and pretty to rush along them.
I hope you all have as good a time as I expect we will. We leave in less than 48 hours for 4 weeks in France.....Paris, Provence and the Dordogne! Yay!