My boys are older, but I've got one reader and one who doesn't like to read. Our local library has an incentive reading program where you sign up, keep a reading log and get rewards for every certain number of hours. You can also put your name in a weekly raffle to win prizes. Check with your library. If they don't have something like that you could do it on your own or with a group of friends or neighbors.
For my boy who doesn't like to read instead of requiring a certain amount of daily reading I require a certain number of books. He likes to read before bed and then he can read more when he wants or less when he's busy. I also try really hard to find books that interest him. He's older and the library also has a teen incentive reading program that's organized a little differently than the one for the younger kids.
Something else I've thought of doing is designating 30 minutes a day for family reading when we all read together. I love to read so I wouldn't mind.
As for math work I would check with the teachers. They often have good websites or workbooks they can recommend. I have not had much luck getting my kids to do math workbooks over the summer. They get very crabby and resistant. So I try to incorporate math into our daily life--math games, cooking and measuring, counting money, playing or working with patterns, etc. Teachers sometimes have suggestions for making math fun and just part of daily life.
Also, I think the kids do need a break from scheduled, formal school work (IMO) so I try to do other enriching activities with them. We go to the Science Museum and the Zoo frequently. My younger son loves to do camps at both of those places and he often signs up for educational camps run through our school district. This has worked for us to keep their brains engaged, but also have some fun.