Levanim. Boys = בנים, pronounced "banim", but with the ל it is supposed to become "levanim". This is the formally correct pronunciation. In daily speech we say "lebanim".
A good way to get around this when writing would be to use the word בשביל [bishvil] or עבור [avur] (both meaning "for the sake of"). Also remember, though, that context is important; if someone is shopping for you, and sends you a text asking what sort of socks you want, and you respond, they probably wouldn't think that you want 12 socks "for the boys" :)
No, but they might have different styles...This is 100% something I would ask a kupait in a kids' clothing store. "Can I help you?" "Yes, I need 12 pairs of boys socks."
So "pairs" is implied? Or else my understanding would be 12 socks = 6 pairs?
Yes, I suppose in this context (as in asking in a clothing store) pairs is implied.
IMHO (a native speaker, probably like BezalelP) "pairs" is not implied. If someone said this sentence to me I'd think they are sloppy, and should say explicitly שניים עשר זוגות or שישה זוגות. If I'd have to guess what they meant, I'd guess 12 individual socks (six pairs), which isn't far fetched if they're all the same color... But I wouldn't be comfortable about this guess.