Check out this dad giving his two-year-old son something he calls a "drum beating". Apparently, smacking a kid on the back makes the best kind of music. No need for guitars or keyboard when you've got toddler giggles to round your sound out.
There were some mentions of this looking abusive, but I think that's ridiculous. In my experience, parents are usually really physical with their kids in the name of a good time. If anything, my girls are always begging me to throw them higher, push them harder, twirl them faster then I'm comfortable with.
I'm guessing by the looks of this kid's big smile, that he is just fine.