Reading about their experiences made me realize that it is completely normal for adults to "lose it" with their children. If we expect to be models of perfect self-control, what are we teaching our children about controlling their emotions, and how will they feel when they can't (either)? Not only can we NOT be perfect, we must try not to beat ourselves up mentally when we are not.
So, instead of feeling guilty or ashamed the next time you lose it, forgive yourself and move on. Try to use your meltdown as a reason to have more compassion for your children when they do it. Little people need realistic models, not of unattainable perfection and icy control, but of human emotion in all its spectacular visible and audible variety. Go ahead -- show your kids how human beings really are, and how they fix things.