From obscure Loire through obscure to obscure Burgundy: Suggestions between

Andrew, Look up Breze Castle, especially if you have a 7 year old. You'll see the majority is underground. This is further to the west in the Loire Valley, but worth seeing. It's off the RS radar. And totally different. IMHO, the western Loire is very interesting. http://www.chateaudebreze.com/ If you like gardens, you should go to Villandry Castle, but I'm sure you already know this. While in the town, you can eat at Les Caves des Gosier Sec. It's in a cave built into the hillside. Inside it smells of wet stone, but your 7 year old will love it.
http://www.legosiersec-restaurant37.com/ Between the Loire and southern Burgundy where you're going is one of the designated European book towns: La Charite sur Loire. There are about 13 used bookstores, and the cathedral, and the local chateau, etc. Here's a link to the book town movement http://webs.schule.at/website/europa/Europa_BookTowns_en.htm In southern Burgundy where you'll be, check out the church at the top of the hill in the village of Montreal, the Grottes d'Arcy sur Cure with the pre-historic cave paintings. In Quarre Les Tombe, a town in the Morvan forest, you'll find 52 stone Merovingian stone coffins around the churchcreepy. This was a center of stone coffin making during the 7-9th centuries. Don't miss the UNESCO designated Bribracte site on Mt. Bouvray. A pre-Roman, Gaullish city is being excavated and reconstructed by teams from different EU countries. When the Roman conquered, they moved everyone and founded Autun, which was a garrison town. Both have Bribracte and Autun have interesting museums.

Oh, Cheverny! One of the best kid events in Europe: the feeding of the hounds at 5pm every day. Don't miss it! In Amboise, you can find Leonardo da Vinci's house, which has cool exhibits and models of his fabulous inventions.

Without looking at a map to see how close you are, I would second the recommendation for Clos Lucé (Leonard da Vinci's house) in Amboise. Absolutely great place to take a 7yo since kids can play on large-size models of Leonardo's inventions. One of my kids' absolute favorites. They also really liked Guédelon - hopefully they're still demonstrating the "hamster wheel" there. I thought the Grottes d'Arcy is in the northern part of Burgundy. It's way cool, but the tours are only in French. Nearby is the quaint town of Auxerre which offers a cool electric vehicle tour, but it might be a bit long for a 7yo.

The Grottes d'Arcy are fascinating, and offer a lot a 7 year would love. The tour was in French, but our gracious guide worked hard to translate into English as much as he could for us, the only 2 English speakers in the group. Other tour folks helped out. I admit, we had no idea what to expect in the "Elvis Room"...gyrating subterranean stalagmites? Blue suede limestone? None of the above. Turns out we were visiting the Elves Room! An English printout is available, there's picnic tables,they sell soft drinks,and paths to walk beside the cave. I believe they closed a few hours at lunchtime.

Personally, I was disappointing in the cave at Arcy-sur-Cure. You surely know of Vezeley, which is hardly obscure, but I do recommend some of the towns of the Serien valley, particularly Noyers. This sounds like a very interesting trip.

Charost is very close to Bourges, a nice old city with a very good cathedral and the medieval Palais Jacques Coeur. You can see much of the cathedral's stained glass close up, instead of far above as is more common. Good walking in the old town and many places to eat etc. Your Huguenot ancestor probably ate there on market days! Second the motion on the hound-feeding at Cheverny if your schedule allows. The underfed dogs scarf up every scrap in a Darwinian frenzy. Not for the faint of heart but great for 7-year-old boys of all ages. Likewise the Clos Luce in Amboise, where Leonardo lived his last years and died. More refined science education for the youngster and fascinating for us oldsters too.