I completely understand that you are responding to scrash's comment about 'dancing' which can be interpreted as referring to the specific gestures and motor actions of the kids, which, as you say, are probably learned. Something as basic as swaying like these kids are can be argued over, but it's not something that I can or I suppose anyone would claim with scientific authority.

When I read scrash's comment though, I interpreted it to mean motion in conjunction with music, not 'this' dance, as you conceded in your edit.

Watch again, and watch the one on the right and snap your finger to the beat of the guitar, it's pretty damn close.

It should also be noted that some people have no rhythm whatsoever, so dancing with the beat would be impossible for a certain percentage of the population at any age.

This is a dubious claim. Motor skills take practice, that doesn't mean that our nervous system isn't hard wired to understand rhythm in time.