This sounds marvelous doesn't it? A number of local groups hold these and take their kids to the beach on the first week other kids return to school. It's a chance to get together, blow off steam and hang out with friends who might have been away or attending too many parks and recs programs over the summer.
C's daughter B has attended these since she was a pre-schooler and it is always a highlight of her summer, time where she can just be silly, put some of the knowledge she's gained together over summer from the various trips to the library and aquarium to use and maybe build a sand castle with a Renaissance flair.
As a homeschooling parent it's a great time to connect with other homeschooling parents and not worry about having a lesson crafted around your outing. Kids learn from each other and now is the time to watch the osmosis occur. It's almost a given that your child and another child will start trading facts back and forth and will use the knowledge gained from this last year to better their sand art or the sand mummification of their friends.