Well typically we sign them up for like 1 activity and then the rest we do family stuff together or just whatever.
However, Austin really likes activities. Thrives on them. He's homeschooled (1st grade in fall), so I don't have to 'worry' about him being gone all day come fall - in fact I'll get more of a 'break' this summer than I will the rest of the year. Kiki never gets to do activities cause I always have her brothers, so I'm glad for them to have some camps to go to so I can do stuff with her too.
So Kiara is signed up for soccer and gym class with me.

Hunter has swim lessons with Austin since we have access to a nice pool for free every day - this is important to me. Hunter also has gymnastics once a week - they did gym in Canada when we were up there with my mom and LOVED it. He also has a montessori arts class, and they're in theater together. He's also doing a nature class and soccer. Aside from swim & gym, they're only one week things, 2 or 3 hours a day. So we don't have too much actually going on each week even though it sounds like it.
Austin has lots to do. Something 4 days of the week from June to August. I think it'll be fun for him, but not something he could keep up with year round - but this way he gets a good feel for what he wants to sign up for come fall. I'm kinda worried about him being gone like 4 or 4.5 hours a day though. That's way more than I'm ever gone from him.
He has (not all at once mind you!)
Swim, soccer, safety town, nature class, theater, montessori arts, vacation bible school, sports camp, junior beavers, science and engineering camp, violin, gymnastics and the reading program at the library. He's just finished Awana this month, next month he finished tball. He starts soccer and football in the fall as well as awana again.
I find I'm more likely to stay home all the time - which is not great for the kids, especially since we're homeschooling. So keeping them doing something outside the house forces me to go out, otherwise they'll end up being unsocialized nerds (like their mama?!). Part of me is excited for all they want to do, the other part is sad that we have so much structure and can't just take off for the beach when we feel like it. We'll be back to more carefree come Sept though.