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.

ココア:
「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.