We just got back from a full week staying at Maya Mountain Lodge with our 3 children - ages 3, 5, and 7. It was a great week. The people were very kind and loved kids. We had a great time hiking in the caves, canoeing in the rivers and climbing up the pyramids of the ruins. We did go to Rio Frio cave which was mentioned in another posting - fortunately, we did not have any experience like that at all. We felt very safe everywhere we went. We had the same guide, Luis Godoy for the whole week. He was great with the kids!! He was very knowledgable and had an archaeology background.
Don't plan on exploring on your own, the roads are very rough and there are no signs. The lodge gave us plenty of water and a packed lunch for every excursion that we did, not to mention the awesome breakfasts and dinners that were included in our package!! The food was prepared carefully with purified water, so we didn't have to worry about any thing that we ate there. They were also nice to bring bread or bananas to the table in case the kids weren't feeling adventurous to try new foods.
Barton Creek Cave was the highlight of our trip!!!