When mine were that age, I always did two outings a day. But when we were at home, they spent a lot of time building and playing with Duplo castle and pirate ship, Playmobil characters and kits, trainsets and plasticene modelling kits.
Endless waterplay in the garden, with their old baby bath set on a low IKEA table, and lots of sieves, sponges, whisks, squirty toys, jugs and boats. Or paddling pool on hot days.
Pavement chalk, painting, crayons or junk modelling - making monsters or space ships. Watching CBeebies or Shrek (about 100 times).
"Baking" with bits of pastry or bread dough I didn't need, or genuinely helping to bake with very easy brownie or muffin mixes. Helping to 'wash' carrots, potatoes and other indestructible veg before I cooked it.
They had wizard cloaks and made potions and cast spells with twigs. Built dens with sheets draped over laundry rack or backs of chairs.
They had giant inflatable beachballs they liked to kick and chuck around the garden. Easy to catch and not hard or heavy if they landed on someone.
We did teddy bear picnics sometimes, on the kitchen floor. Or outside if sunny.