tattletale

伊坂幸太郎氏の小説 "Remote Control" を読んでいます。パート4，The Imcidentから引用します。

On days off, I make deliveries for especially for good customers on my own, charge them a lower rate, and everyone makes out--except the company, The guy on the phone said they knew all about it, and they would tell the company if i didn't cooperate. Feels like a fucking grade school tattletale, except they'll get me fired right when my daughter's starting all those expensive girlie lessons.

"telltale" と似ていますが "tattletale" の意味を辞書で確認します。

・Oxford English Dictionary: a child who tells an adult what another child has done wrong
・Collins Dictionary: a talebearer or informer, esp. among children
・Cambridge English Dictionary: a person, especially a child, who secretly tells someone in authority, especially a teacher, that someone else has done something bad, often in order to cause trouble: She has good manners, yet tends to be a bit of a tattletale at times.
・Vocabulary.com: A tattletale is a person who tries to get someone in trouble by revealing secret information about them. Your tattletale brother will probably tell your parents that you were actually at the movies, not the library.
The word tattletale is mostly used in the U.S. (in Britain it's more common to use telltale). It comes from the verb tattle, "report someone's wrongdoing." In the 16th century, you'd have called a tattletale a pickthank. These days, you can also use words like snitch or whistle-blower.

"tattletale" は普通は子供について使うのですね。