Japanese by Example
Learning through examples in manga

Don't underestimate bread-baking with 〜てはいけない

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Cocoa tells her friends they mustn't underestimate baking bread. Rather than prohibiting them, this gives the sense that it would be wrong to underestimate the process of baking bread.

「みんな パン(つく)りをなめちゃいけないよ!」

Note that ちゃ is a casual spoken variation of ては.