"Ça va bien les garçons ?"
"le" is singular: le garçon (vowel pronunced like "but")
"les" is plural: les garçons (vowel pronunced like "bet")
It accepted "Are the boys well?", but the meaning is very different. Is it right? Is there a more usual way to ask the health of someone not present?
Actually, you are right, the sentence in French can be about absent boys as well as asking the boys themselves how they are doing. I assume a bit of context would differentiate that ambiguity quickly enough.