"You are boys."
Translation:Vous êtes des garçons.
Might help to think of possessive determiners like mon as an article - if you think about it, mon implies 'the'. Mon cheval means you're talking about a specific horse, the person you're talking to could refer to it as ton cheval or just le cheval, either way it would be clear which horse they meant. Mon le cheval means 'my the horse', which isn't done in French (or English, of course!)
I'm a beginner with French, so I'm not sure how accurate this idea will be (hopefully someone will correct me), but I think the rules in French are pretty much the same as English when it comes to determiners and articles - we always use them, with one exception: for whatever reason, in English we drop the requirement when it's an indefinite plural. Like this:
There is a cat here
There are cats here
You are a boy
You are boys
When it becomes plural, the indefinite article a just disappears. You can put some in there, as in "there are some cats here", but it's unnecessary. It's already implied. "You are boys" really implies "you are some boys", we just don't say it (and it sounds a bit weird to do so). French is more consistent and keeps it in, so you get des for plurals.
The last two items in French conjugation of the verb être (to be):
- Vous êtes (you [plural] are)
- Ils/elles sont (they [masculine/feminine] are)
You wouldn't say Elles êtes nor Vous sont becase that's mixing up the terms. You wouldn't say Ellos sois or vosotros son in Spanish either.
Yeah... It's very much that you are trying to use the tense you would use for "ustedes" in Spanish with the pronoun "vosotros"... You need to think latin America love, where they use "vosotros" instead of "ustedes", from what I've gathered - not that I think this applies to Guatemala or Honduras, sadly for us. <3