HERE ARE THE LYRICS:

Ring-a-round the rosies,
A pocket full of posies,
Ashes! Ashes!
We all fall down.

This story it's incredibly scary and it's just unbelievable if you think you can match it with one of the most popular children's game.

Unfortunately the real story has nothing to do with children but it's all about hte bubonic plague that killed around 200 million people 7 centuries ago. So why "around the rosie"? It's not actually about a rose but you can probably match this part with one of the common signs of plague disease: the rash like a ring on the body, a red rash usually with a black circle around it. Quite creepy.

The "posies" inside the pocket can be indeed associated with the fact that people usually kept wearing flowers to cover the stink of death they usually had, also most of the people thought that clearing that bad smell somehow the disease could vanish as well. Everybody, at that time, thought that black plague was also spread via bad smell.

Likely the words "ashes ashes" refer to thefact that, at that time, they used to burn dead bodies of the people affected by that disease so this is a really macabre part just like the last one: "we all fall down" which is clearly concerning the death.