They won't do swimming, by my understanding.
We used them on our last trip and I would definitely use them again. Our only issue is that my girls are much older than yours (almost 9 & 11 at the time of the trip) and they really enjoy younger (late teens-early twenties) babysitters. I requested a younger sitter and was told they would do what they could, but made it very clear that they couldn't promise anything. When our sitter showed up, she was definitely grandmother age, much to my daughters' chagrin. She was very nice and very responsible and I had no worries at all with leaving her with my girls, but she wasn't very much fun. I think she wasn't into the 'tween age too much. Having said that, I think KNO would be perfect for younger kids! I wouldn't hesitate to use them again.
Have fun on your trip!
Leslie