We keep learning all year-long. In the summer I like to be particularly playful and weave in academics organically. One of our favorite new games is to draw a chalk number line at the park. My daughter jumps by 3s, backwards on odds. Or we add - stand on 4 and add 3! My son jumps from number to number, counting aloud and backwards. It's a great spin on hop scotch, and fun to warm up in the sun after the pool!
Another fun project is to set up a scavenger hunt to collect elements of nature. After they have the correct number of each item, they can add and subtract them from each other. We used our five flowers and added 3 leaves. Chalk is a great way to introduce addition and subtraction signs.
Outdoors is great place to practice telling time. Using a hula hoop and some sticks, create a clock. Every once in awhile tell your kids the time see if they can replicate it on the clock.