I agree with everyone that it is not a need, but something that the kids will likely enjoy.
My kids not only go to day camps, they started sleep away camps since 7 and 8. They are 10 and 8 now. This summer, they will go to the camp at Seaworld.
However, be careful in evaluating options, everyone's budget is different. If the budget is tight, don't feel you have deprived the kids of anything. I always told my kids I didn't have the many "necessities" they have now. If you do want them to have the opportunity, many places may have financial aids.
Also while the kids may have fun, but it may not be the best value for the money spent. For example, last year we paid over $600 per week for 2 kids including after care for a local YMCA. It included swimming. Last year, I happened to have time and decided to go to the pool to see them, what I found out was that they have to bus the kids from the park to the pool, and have the kids swam in the pool. It ended up many of time, including my girls, were just holding on the side of the pool to talk. The after care was just a bunch of kids throwing balls among themselves. We didn't have too many choices, as both of us work. If I were not working, I would have a better use of the $600 for one week.