Hi - regarding your daughter - I don't really know about libertarian thought - but I am a post modern thinker, and my view is that regarding children - the parents have to educate their kids in a clear pathway but to allow them freedom of mind whenever available so they will keep their mind open and will not stick to ideologies that they did not think about - the final goal of this way of education is to shape a whole person, but one with criticism and open mind, so that when the kid gets to an age adequate for self decisions and deep thoughts - he will think over what he was used to until now - and decide whether he want to continue living according to them, or his opinion is now different and he want to go in his own way.
now, regarding to your girl eating all of the m&m's - I think that's actually a good thing :) letting her decide what fits her and what not in a topic no disaster can emerge of.