First day on the Au Pair job... HELPP?

So long story short, I started as a nanny today (I'm still in highschool) with this family of two boys and a 16 year old girl. Their dad just passed away, so I felt this tug at my heart to help. They live in a very unstructured environment, and are understandably a little confused as to how to behave. I grew up in a strict, structured environment and I told them right off the bat that they were going to respect me and be polite and obedent. They were perfectly fine until the sister came home, when they thought they could get away with every thing again. The little boy demanded a snack after dinner, which I told him he could have if he said please. He threw this HUGE tantrum - banging his head against the wall, punching and kicking me, and all while his siblings were watching. This went on for about an hour. The mother came home and I said a quick goodbye but I know she saw the tears in my eyes, when I definitely just broke down on the way home. This is my entire summer, and I know everyone has walked out on this family, I don't want to add to that (the father killed himself), but its only my first day and I'm at my wits end....