I bought my two a book from M&S called Bright Sparks BIG English maths and science book. They did three different books for different age ranges. 6 yr old dd has really enjoyed doing hers sitting by the pool, waiting for us to finish dinner etc. 9 yr old ds does one page a day from each section under duress which takes him max 10 mins. He has no homework all summer which I think is as it should be but I don't think 10 mins a day is too much to ask and hopefully it will stop his brain going to mush.
The reason for my post is just that I'm really pleased I got these books and I'm assing that there might be other parents like me looking for something similar for the summer holidays. They are a good size, the content seems well produced and very varied. I'd definitely buy them again next summer.