depaato de wa, kodomotachi ga esukareetaa de asobanai you ni, tenin ga yoku mite iru.

At the department store, the staff watch carefully so that children don’t play on the escalator.

Breakdown of depaato de wa, kodomotachi ga esukareetaa de asobanai you ni, tenin ga yoku mite iru.

• は: topic particle
• 見みる: to watch
• が: subject particle
• で: location particle

Questions & Answers about depaato de wa, kodomotachi ga esukareetaa de asobanai you ni, tenin ga yoku mite iru.

Why does the sentence start with デパートでは instead of just デパートで?

では is で + は.

• で marks the location where something happens.
• は adds a topic or contrast nuance.

So デパートでは means something like:

• in department stores
• as for department stores
• at department stores, ...

It often sounds a little broader than plain デパートで, as if the speaker is talking about what happens in that setting in general.

In this sentence, デパートでは sets the scene: In department stores, ...

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Why is it 子供たちが and not 子供たちは?

Here, 子供たちが marks children as the ones doing the action in the subordinate clause:

• 子供たちがエスカレーターで遊ばないように
• so that children do not play on the escalator

The particle が is natural here because it identifies who would do the action 遊ぶ.

If you used は, it would sound more like you were making children the topic or contrastively talking about them. That is possible in some contexts, but が is the normal choice here inside this kind of clause.

So:

• 子供たちが = children are the ones who might play
• 店員が = store clerks are the ones who are watching

The sentence has two separate が subjects in two different parts of the sentence.

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What does 子供たち mean exactly? Is たち always necessary?