What to do?

So, I currently work for my aunt and uncle as a nanny of sorts while I attend school here in Southern Utah. My three cousins that I tend (Alexis, 14; Valeria, 11; and Leland, 9) are usually pretty good, and we have a lot of fun. All today though, Leland has been throwing a tantrum. I don't know really what to do because I can't physically do anything, and my words don't mean anything because when he gets in one of his moods, only his dad can make him listen, and even that is only sometimes. So tonight, after hearing that I am not wanted here, that I don't know how to do anything, and having things thrown at me repeatedly (all by Leland), I am completely worn out and just don't want to do this anymore. My uncle Marty didn't call me back to deal with the issue for almost two hours and the whole time I was pulling my hair out, trying to stay calm. I hate having a temper, but at least I can keep it under control most of the time. So now here I am as I'm finally getting around to my homework, since I was otherwise occupied all afternoon, and am frustrated with everything and it's throwing off my concentration. Good thing tomorrow is another day, and I can only hope that it will be better.