not just kids...at my archery range you can get arrows by the dozen. The price is listed as $2 for 12 arrows. People will walk up and hand me $4 - and the conversation goes like this.

me] 'You'd like two dozen arrows?"

them] - NO, I'd like two sets of twelve.

me]So you'd like a total of 24 arrows.

them] No, I want 12 and another 12 for my friend.

me] two dozen then.

them] - no, two sets of 12 please.