I'm assuming that you've already - at the time you signed the children up - explained that you would be taking time off? If not, you must do so immediately so they can arrange alternate care for their children. If you've not told them prior to now that you will be doing this, then I think a month's notice is called for. If you've discussed this in the past, 2 or 3 weeks ought to be alright. Do not be surprised though if when you get back from your trip, you don't get all the kids back. When I was a working mother I could not have put up with having alternate day care. They may indeed find someone professional who, if she has to be gone, has someone available to take her place. Someone both the children and the parents know and trust. If you have a temporary replacement lines up, then make sure she/he meets the parents approval and is totally reliable. Until all these requirements have been met, you shouldn't go, unless of course this is because you actually want to stop doing daycare. Don't think I'm implying you don't deserve a vacation. You undoubtedly have a family and you and they need this time away from work. It's just that as you are working as a provider, you must do it in a professional manner. Have a great trip!
