Why - Fontainebleau first of all, has the most amazing bouldering I have ever done. It is HUGE with so many bouldering areas it would take you at least half a year to see all the boulders. The boulders have some of the most famous amazing lines and slopers in the world. The landings are sandy. Did you hear that? SANDY! So, your kids can play with shovels and buckets and cars and be occupied for at least 6 hours simply playing in the sand. The boulders are also in a magical forest of entertainment for the little ones, with plenty of small sized boulders for them to run and jump and hide and imagine around. And lastly, it is only 30 minutes from Paris! That leads me to the "where" information.
Where - Being only 30 minutes from Paris, France means you can stay far enough in the countryside to enjoy some peace and quiet and simplicity with the kids, but it also means a short train ride to one of the most amazing cities in Europe! The boulders are located in a large dispersed area, with
When - I'd say fall is probably best then spring, but you really can climb there year round. We went in July, fearing hot temps, but were quite lucky and it was never hotter than about 76 degrees. We've been in November before, which is great for visiting Paris (no crowds), but we had snow and lots of rain.
Accommodations - My favorite part about vacationing in France is the plethora of cheap accommodations! We always rent a gite, which is a restored farmhouse. They are basically houses where you can cook your own food and have your own yards etc typically, and can rent for seriously as cheap as 100 euros a week! Depends on how large, how nice, etc you want. We stayed recently at this gite. You really should use this website to search through all the gites throughout France. We have also stayed at this B&B directly in the city of Fontainebleau, and loved it. . We have also stayed in the IBIS hotel chains in the area, and many other gites, but this latest gite was definitely in the best location. Very close to the Three Pigeons Climbing area (see Bouldering Areas section below).
Food - Having kids, we tend to always stock up on groceries and eat in as much as possible. There is a wonderful Carrefour VILLIERS EN BIERE Route Nationale 7, 77190 Villiers-en-Bière, France. Think massive Walmart, only 100 times better, and in a fancy schmancy mall. They seriously have 2 aisles just of cheese selections! This place really is amazing. And they sell my favorite French kids clothing line, Le Petit Bateau, for much less than the boutiques sell it. There are also lots of pizza joints you can call for carry out, and plenty of great restaurants around the area. We really like a Chinese Restaurant in Bois Le Roi called Grand Bonheur. In Arbonne La Foret is a good climbing hangout/pizza joint called Croq Foret. Also good. And don't forget to get Pain Chocolate at a Patisserie! I LOVE french bakeries. Nothing compares.
Bouldering Areas - For in depth bouldering info, go to this website. Personally, my favorite area to go for amazing intermediate problems (V2-V5) is Three Pigeons area. This area is also pretty ideal with kids because of the sand. It has TONS of it. Feels like you are at a beach in some parts (e.g. by the Cul De Chien).
What to do in the Area - Aside from bouldering, there are castles and medieval cities, Paris, museums galore, and plenty of nature hikes and exploring to do. I would devote at least 3 days to see Paris, but spread the visits apart! It can be a little stressful/overwhelming in the summer with the huge crowds. There are dozens of things to do with kids, but I really like this summary list of the top ten things to do in Paris with kids.
Vaux le Vicompte is an amazing little castle near Melun that is definitely worth checking out. You can rent a golf cart to drive around the awesome gardens.
Does that cover it all? If not, let me know and I can add more to assist you if you plan on visiting the area.