My contract require 2 week notice of closures. I typically let client know as soon as I know. The more notice I can give, the better. It up to you what you do. You know your client and their situation. A parent with no local support, or who have a min wage job which can be less flexible than a senior member of staff, might appreciate advance notice so they can try and find alternate care or book leave themselves. As long as you meet the term of your contract, I not see any harm in giving extra notice.