Learn French: Ne nous fâchons pas devant les enfants. - Let's not get angry in front of the children.

In affirmative commands (when you tell someone to do something), the reflexive pronoun goes after the verb with a hyphen, like fâchons-nous (let's get angry). But in negative commands (telling someone not to do something), the pronoun moves back to its normal spot right before the verb. It gets sandwiched between ne and the verb: ne nous fâchons pas.

The English translation says "Let's not get angry." Where is the word for "let's"?

French doesn't have a specific word for "let's". Instead, you just use the nous (we) form of the verb as a command. So, saying fâchons ! means "let's get angry!". To make it negative, you wrap it in ne ... pas, resulting in ne nous fâchons pas.

Why use devant for "in front of"? Could I use avant?

No, because they measure different things! Devant means "in front of" in physical space (like standing physically in the presence of the children). Avant means "before" in time (like happening before 8:00 PM).

Why does this verb need a reflexive pronoun (nous) in the first place?