Wiktionary
tell tales out of school
alt. (context idiomatic English) To reveal confidential or sensitive information; to gossip. vb. (context idiomatic English) To reveal confidential or sensitive information; to gossip.
Usage examples of "tell tales out of school".
You tell tales out of school and I'll beat your ears off with an ax!
I assured him he might depend on me not to tell tales out of school.