How to quit babysitting job?

She has 2 children, 3 and 6.

1. They fight allot. Pulling hair, hitting, with pillows and laundry baskets too. Swearing (6 yr old dropped the F bomb) and they just don't get along.

2. I'm constantly having trouble getting the toddler to bed. I have over 4 years of XP with toddlers (I'm 16) but this chicks crazy. Just tonight, she finally got to sleep at 11, 2 hours past bed time and I did everything and more than what Mom told me. She tells me not to stress if she doesn't sleep but as a sitter, it's my duty to get them to sleep, you know.

She spat at my face countless times tonight, hit, kicked, BIT and licked. Threw her bottle at me along with many other things she could get her hands on and drew on the carpet -_-.

Toddlers are hard, but here's the thing. I am the primary sitter for this family and 2 others, quitting this job wouldn't kill me. And I feel bad because the parents go out allot, like, they need breaks.

How do I quit politely? I feel a bit bad...2 weeks notice?