Personally I'd take two weeks off of the summer holidays and add them onto the Christmas break. From what I've seen, most of the kids (mine included) are bored out of their minds by the end of summer, and are pretty exhausted by the time the Christmas break comes, and not quite back to 100% by the end of that break.

I'd say it's fine as it is with them not going off until almost Christmas, so they're not bouncing off the walls, but currently they go back 2nd week in January and I'd say they could do with having until around the 20th.