Not sure what the weather is like in MO during the summer, but what WE do or have done, I can tell ya. Our routine last summer was basically this: Mondays: "open" day, except swim lessons late afternoon (4-5)
Tuesdays: we would go about 9:30am to the playground behind the library and play there, get the kids running around and "tired", then walk to the library for storytime and a craft at 10am, and I'd quickly choose 7 books and 2 dvds for the week (for time at home with the boys). After storytime/craft, we'd jet over to McDonalds (one block away) for small fry club. It gets VERY hot in TX summers, so we liked indoor playlands and this particular McDonalds had a massive indoor, air conditioned playland with a good toddler area as well as the normal stuff, free basketball games, air hockey, some video games, and small fry club was a once/weekly meeting for little children. The leader was great, and she'd have a story or song, then a craft or game, sometimes a special guest like the fire fighters, Ronald McDonald, etc. The moms would hang out and chat (made a very close friend from there) while the kids played and ate lunch. Then it was home for nap and "homemaking".
Wednesdays: Bible study in the morning (with great, free childcare at the church that the boys loved), and then lunch or coffee with the ladies (Bible study was 10-11:30 but childcare was free from 9:30-1:30 so we could have some time to spend together). In the evenings, swim lessons.
Thursday mornings was a free movie at one theater or $3 at another (summer movie specials where they'd show a different family movie every week, again, for air conditioning). My 3 year old LOVED going to the movies (it's all moms with little kids, so it didn't matter if they weren't perfect, but they have come lightyears in preparing for children compared to how they were when I was little: child snack trays that clip onto comfy booster seats are so neat. The rest of the day was open.
Fridays: a playdate either at my house, my good friend's house, a playground, or the spraypark in the mornings, and swim lessons after nap and a snack.
Saturday: family fun day (we would wash our cars, but otherwise it was just fun at the neighborhood pools, botanical gardens, a special event like an air show, neighborhood event or block party, a special showing at the museums, hot air balloon fest, really just whatever came up. If nothing was happening that weekend, the pools were a happy choice).
Sundays: church, chill (or have someone over for lunch), do all laundry in the house to prepare for the coming week (my husband would iron and I would do a lot of cooking).
On all open days or open chunks of time, we could do stuff around the house. I got a big roll of paper (like butcher paper) at an office depot or staples or wherever...a BIG roll of white paper. I'd spread it on the coffee table and cut it to that length, stick a little masking tape on to hold it still, and then the boys (mine, and sometimes his friend) would be able to color or draw on it, or play-doh without making too much of a mess, or even finger painting if I was going to be right there to help. Sometimes we'd do other little projects and then when we're done, you just untape the paper and roll it up, toss it....super easy cleanup! We had a little baby pool that in the backyard for the baby and I to sit in and play splash together while my older son and his friend would play "whatever" around us. When it got too hot for that (once it started hitting hundred degree weather all the time), I dumped the pool and washed it out, brought it to the kids' room and filled it with multicolored balls you can pick up in a big black bag at Walmart, Toys R Us, or craigslist. Made our own ballpit indoors. The baby loved that, and I stayed to help him support himself, and the 3 year old loved it too. Sometimes the big boys would have "war" where they'd throw the balls all over the place at each other, and I was fine with that, but put the safety gate on the door so my little one wouldn't crawl in and get trampled. From our house we could walk to the pond to feed ducks or fish, a playground, and a spraypark. We did mostly water or indoor fun if it was 100+ outside. We purchased membership annually to a couple art museums and season passes to the zoo. The zoo passes are awesome since it wasn't very far because we could visit for an hour or two, and then leave. No stressing or pushing to see everything in one day, because we can come back in a couple days and start on the other side the next time. I was big on getting our neighborhood magazines and making a monthly "plan" involving any special events that we thought might be interesting, for our open days or big chunks of open time, or for weekends too (hot air balloon fest, airshows, car shows, live theater for adults OR children, kidfish events, something fun at the stockyards, a new exhibit at any of the million museums around, etc). Now I live on the east coast in a really small town, but it's got a beach! Currently working to see what we'll be doing this summer. Right now my oldest son (4) goes to daycare which he calls school Mon, Wed, and Fri. Mon and Sat are soccer games but they end June 4, Tues and Fri are kung fu, Wed is Awanas (but that follows the school year so it ends in May), and the baby (16 months old) goes to kindermusic and storytime at the library with me while the older brother is in "school".....thinking swim lessons for both boys to replace soccer and kindermusic, starting in June. Keeping Kung Fu. We will be going to the beach regularly, and trying to explore the nearby towns to see what's available to us (Savannah, Charleston, Columbia, whatever)...somewhere that will have museums and stuff to do for weekends with the family....but I plan on playdates, exploring the nature preserves, swimming, and fun activities at home to be the bulk of our summer fun now. It's a change of pace to have a lot less stuff available, but there are still things to do. Just gotta find them. We'll carve out our new niche soon enough. :) The beach, I suspect, will play a huge part of our life now, and that's pretty awesome.
Now we're on the east coast