You are aware that 6-10 year olds spend time around adults and other kids older than they are right? Did you never pick up anything from an older sibling or kid at your school?
My 4 year old has all sorts of isms and habits he learned from me and my wife, aka his parents. There are tons of explanations beyond “all slang is the result of parents too lazy to raise kids so they drop them in front of an iPad.”
We live in a society (seriously). We have communities. People spread language and customs every day between each other.