I've been focusing more on reading. We take weekly trips to the library. They each pick out a book. My readers will either read aloud or silently and tell or write their favorite part of the book. My non reader will get read to by the others or myself, & will also tell her favorite part.
On their own, the boys have found resources for them to learn history and science online while incorporating fun activities & games. And math I use with them on a daily basis whether at the store or measuring in the kitchen.
We'll play games like scrabble to enhance spelling skills, UNO for numbers & colors & directional skills (for the younger one). In the mix of these things they've also chosen to learn guitar, so we have a DVD they put in and will follow along for about an hour.
Education is extremely important to me and I want them to understand that even though it's summer doesn't mean they have to stop learning, & they don't have to compromise their fun. :-)