I'd give a months notice, more if you are willing and able to lose clients before the move. It's up to you what you say about the reason for the move. Keep in mind whether or not your parents would be chatting with you for the last month...are they the type to ask where you are going and how you feel about it etc? If so then just tell the truth...your husband felt it best to switch careers so you all can stay in one home, near family when you have 2 children. They may get annoyed at first but it's just a fact of home daycare.