Quitting babysitting job?

I'm a full time babysitter/nanny for an 8 month old and 5 year old and I'm due in the first week of March. I'm wanting to work for these people up until I give birth and then i want to quit and get a part time job instead of returning from unpaid maternity leave. I'm only getting $50 a day and I'm working about 11 hours a day 5 days a week. It's honestly not worth it to me and I do not want their 5 year old around my newborn. She's not a good child at all and their baby is super attached to me. I'm going to feel awful telling them I'm quitting though and I have no idea how to do it! Have any of you been in a similar situation? How do you quit from a full time babysitting job? I was planning on telling them I don't want to come back a week or two after my baby is born so while they have their temporary childcare arrangement (they still don't have one set up) they can find a permanent one. Does that sound reasonable? She was expecting me to take 6-8 weeks off anyway and at first I was going to come back but now I want to return to college and get a part time job. I feel that I could make similar amount of money working shorter hours and I would love to go back to school.