Do you think I should just leave it be?

Okay so I think my sister is growing up way too fast. She's only 10, has Facebook, a cellphone, stays home alone, walks home alone from school, sits in the front seat of the car, there is definitly more but i cant remmember right now. She doesnt do things she should be doing. and the thing is my parents don't mind! My dad offered to buy her a computer. My mom doesn't say anything to her when she stays up until 12. They were gonna leave her home alone while we went to a neighbor state for a couple hours. It annoys me so much! I'm 15 Now, and most of my stress is caused because of that. Oh & my FOUR year old brother gets to go to bed whenever he wants as well. And they're both spoiled materialwise. What do you think I should do? Just let it go?