When they sign the contract I take a two week deposit which is kept and applied to the last two weeks of care so while it might not be the money for my entire 4 week notice period at least it is something. It has been a long time since I had a client pull out without notice or payment so a lot depends on your area and how likely the clients are to just disappear.

Another option is to have them pay for a full 4 weeks but the money goes towards both the first two weeks and the last two weeks. But you expect payment two weeks in advance so when they start they will pay for the third and fourth weeks they are with you if that makes sense. Then in reality you will have the full months payment as it is all in advance. I had intended to do this but found by the time parents are 3/4 through maternity leave money is getting tight because they never lowered their standard of living to reflect the loss of income plus expenses of additional child so getting the two week deposit is all some can afford.