Up until third grade, we really had very little options for local summer camps for the kids. They would go to the local YMCA or things like that. The local university would offer some science-oriented camps, which were so-so but all we could do.
Starting in fourth grade, our local community college offers accelerated summer classes for children. My older child will do it again this summer for the third summer, and our younger one will do it for the first summer.
They have to take an above grade level exam like SCAT to qualify.
They have one-week classes for 5 weeks for the younger one; five week classes for the older one. They only go 9 am-noon, so you have to drive out to the community college in the middle of the day to pick them up; no day care!
The younger one will take probably science and one math; the older one will take Algebra I and something else.
The classes are expensive ($300 per week for each) but they are really well-done and the kids love them.
Eventually, I think they will take some summer classes at Stanford, when they are in high school, to check that out.