She's 6, even if she needs arresting (and that's a rather big "if" there), she's tiny, she doesn't need handcuffs.
The person who did that needs to have their head checked. From the video they did not appear to be wantonly cruel, they appeared to be some sort of rule following robot, without a brain that says "wait - she's 6, let's not do that".
But this is not some normal thing in the US.
It probably also helped that I am white and 50 years old.
When I was in 4th grade a student pushed another through a glass door, cutting her leg open. Kids tripped others down stairs.
America is violent, it starts young, and it’s perfectly normal in a lot of places.
But Florida, being Florida, is likely more slave patrol outside the larger cities and tourist areas.