Two boys are plotting something wrong.
A: I’ll go out after your mother goes to bed.
B: OK, I’ll come! Mum won’t know.
In this situation, what should you say “Mum won’t know” in Japanese?
Casual
B：母さんにはバレないさ
Note: This is not a word-for-word translation.
Advanced Tips
A word-for-word translation
B：お母さんには知られないから
You can also be said as ママ, おふくろ, お母さん for Mum.
ママ may give an immature impression, and おふくろ seems to be easy for men to call because it’s not too formal and has no immature connotations.
お母さん is the most popular way for both men and women to call their mothers.
Kotoba no Hibiki 