Play - like literally turn everything into a game that you do with the kids, cooking, cleaning, tidying up, kids of any age can get involved in some way even if it takes a bit longer.
Have a hobby around the house- gardening, knitting, whatever takes your fancy, bonus points if your kids can get involved. Nothing tires them out more than fresh air and digging in the dirt
Get a dog- walks, training, again with the kids, great for getting them knackered.
Basically keep the little ones outdoors and moving for as much of the day as possible, they will learn things, have fun and there are less things to tell them no about so fewer tantrums, and the fresh air means at lunch / snack time they will sit quietly with their food and a colouring book so you can have a decent coffee break
Honestly I love being a SAHM, thinking of activities amd games, splashing in puddles with them, getting the admin done in between, its all brilliant