Your kids are all still pretty young. When my son was about 4 his older sister (age 7 at the time) asked "are we ever going to eat at a restaurant again?"
Sometimes the effort of kid-wrangling is just not worth the needed trip out. I used to grocery shop when my husband was home or my mom was there. Or if I had to bring a kid I'd only bring one. I never went clothes shopping with the kids, or even to Target. I stopped going to the beach as one kid would run in one direction, the other kid would try to eat rocks, etc.
I found a few playgrounds / parks that worked well with the kids at their ages - I had a favorite that had benches in the shade and I'd pack lunch, snacks, drinks and settle in for a couple of hours. I'd call friends to let them know where we'd be and often at least one, sometimes more would come with their kids. It was a great way to get out of the house and it allowed the kids to stretch their legs, run & jump.
On the really hot weekend days I'd call my sister and ask if I could come over (my husband being a rookie police officer at the time rarely had weekend or holidays off so I was on my own!) She had a pool and a fenced in backyard with a great wooden swingset/fort. The kids could spend hours in the pool and I could control the situation (unlike the beach) and there were other adults and teens who could help me.
In the winter I'd take them to Mc Donalds mid-day and get them happy meals and they'd run around the kids play area while I read the newspaper.
On bad weather days when I didn't have the $ for McDs I'd allow them to make forts in the living room using blankets, sheets, couch cushions, chairs, folding tables, etc. They were only allowed the one room to "destroy" and when done we'd all fold balnkets together, and get the room back in order, etc. I would crawl through their caves / forts with them and we'd lay down and read books together. My son took a nap or two in the blanket forts over the years. ;o)
I've heard it said that taking kids to the store is like tryin to herd cats or it's like bringing a few goats. Give yourself and the kids a break. Forget the organized activities unless you know it's a safe place for them to run and climb. Scout out the best parks around, let the older one bring a friend so she doesn't feel "too grown up for that baby park", bring scooters or tricycles, pails and shovels, etc.
This season will pass - it doesn't seem like it now as it's physically exhausting and you don't see a light at the end of the tunnel. But they're teens before you know it and then the challenges are emotional and you'll be exhausted in a different way. I miss the days of couch cushion & blanket forts - but I do love the kids my children have become as teens. The next season is coming for me too - one more year til the first goes to college. The time just screams past me...