People need to calm down. This isn't a school dance since it's being held in an apartment building. Also it looks like a birthday party and what was recorded was a "dance off". They weren't dancing like that the whole time. The adult I'm sure thought it'd be funny if they emulated adult dancing. I also highly doubt it's even in the US. Phones with cameras exist in other countries as well. Everyone here was trolled by the title since it was meant to get a rise out of people.
I'm so glad videos or threads like this immediately bring out the anti-immigrant sentiment in these forums. It's like clockwork.
I'm sorry, did you just say it's ok for 8/9 year olds to be grinding? Regardless of where they're from?