Walking in the Common today with DC (neither talking yet) I overheard a couple very sternly correcting their 4/5yo child for calling out "I want...." They both told her she should say "I would like...".
Personally I don't see anything wrong with "I want.." if the tone's right and there's a "please" included.
Surely if you're going to be that pedantic you should insist on "May I have....". Or did I miss out on a vital lesson in Manners 101?