We use down time in the summer for lots of board games (we live in FL so heat is an issue here, we do have a pol but you can only swim so much and the water is 90 degrees so more like a bath than a pool). We also pick a topic to read about, like dogs, and learn lots of stuff about dogs and try to teach our old dogs some new tricks etc.
I try to plan blocks of time, say from8-9 outside while i’s cooler, 9-10 we will bake or make something in the kitchen, 10-11 read, 11-12 chores, 12 lunch, read or board games after lunch, 2-3 quiet time, 3-4 turn the music on and dance or just enjoy listening, 4-5 chores and dinner prep, after dinner when it is cooling off again back outside……..bath, bed
Most important just have a plan…….
Not sure how old your kids are but mine like doing inside things like putting a sheet over the table and pretending its a boat, cave whatever. Or we go into the darkest room or closet and have flashlight wars………we have some wooden indoor bowlinf pins (etsy) and we use our hallway to bowl……books on tpe while coloring……..make tents in the family room………some things make a more to clean up, but then the clean up kills some time too!