This is what I do, very similar to Transylvania Mom - my kids are 2 and 5 and very energetic!
We have a rhythm to the day. Breakfast, get dressed, out the house by 9.30ish. I have a list of places to go - splash park, regular park, bike park, farm, library, aquarium, outdoor museum, water slide, etc. Everywhere is either free or we have membership. I bring snacks and water. I have a bag with sunscreen, hats, diapers, etc. Sometimes I pack a picnic lunch but usually we are home back by 12.30. Lunch at home. Rest time from 1-2 for older one. He listens to audio books in his room. Little one sleeps until 3 or 4. When big one gets up we go outside the house. He tries to find neighbours to play with. 5pm come in, make dinner, eat, bed by 7.
I would just pack a simple bag the night before and plan to leave the house after breakfast. I'm sure you must have nice parks near you.
Also, my 5 year old goes to a very low key drop in camp at the rec centre twice a week. It's cheap and simple and he loves it. Is that an option?
Oh, another thing, how about water play? I bought a cheap paddling pool and the kids LOVE it. They and their friends can spend hours playing with the water. The sprinkler is also a big hit on a hot day. If you have a big enough yard you could get a slip and slide. So much fun.