My 6 y/o and 3 y/o did for a little awhile. They LOVED watching playdough videos. There was an article came out recently that there are some extremely disturbing videos on YouTube Kids like how to taste battery acid, or juggle knives and videos with jokes about pedophilia/drug abuse. I can't always monitor what my oldest watches, so I deleted the app on the kids iPads.
I really hope they didn't watch anything horrible 😁 sometimes the only way I can take a shower is if they get 30 minutes of iPad time!