When my kids were smaller, when I would watch tv or play with the kids, I would lay on my back and balance them on my bent knees and pretend they were on a horse. They loved it. I would hold there hands to keep them from flying off. Another thing I would do, when doing push ups I would tell them they had to crawl under me when I pushed up (I was the bridge, crane whatever) otherwise when I would come down they would be "squished!" Think outside the normal routine. There is a lot of sweat to be had. Good luck.