When do you use bebem or bebemos

the boys drink water?

It's the "m", "n", "ng" sounds I have a problem with. When there is an "m" in the middle or end of a word it usually sounds like "n" or "ng" to me. But it's hard to be sure.

Does this sentence sound right in Portuguese without an article at the beginning? In English it does sound right "Boys drink water" as as generalization about boys, but in Spanish it would always be "Los niños beben agua". What about Portuguese? Shouldn't it be "Os meninos..."?