Hey Erica
I do home child care also, and if it where me I would not give your parents a set amount of weeks just yet. I know they probably would like to know so they can make plans. I just think having a baby is one of those things that can't be planned and organized in all facets. Wait and see how the delivery goes, and what the baby is like. Most babies don't sleep through the night until they are 8 weeks or so, so you may be to tired to have kids come back. If you end up having a hard delivery or c-section, or the baby has colic you may need 10 weeks. I would not commit to any thing yet. I would tell the parents to plan on 4 weeks and at three weeks you will touch base with them as to how things are going and how many more weeks or not they may need a different care giver. I would also take into consideration the kids you watch, how demanding are they, do they listen (they will need to be quieter when the baby sleeps, will they understand), they may need to wait longer for things because baby will need to come first. Will they be nice to the baby.
I know it is hard to think about 6 weeks w/o pay, assuming you are not charging the parents. But you know the kids you watch better then anyone, so how soon do you want them back while getting to know your new baby.
Anyway, thats how I would think about things. I hope this helps. Good luck! Let us know what happens. I really hope you have an awesome easy delivery and a healthy happy baby. Best wishes to you and your family.
T.