My ex husband says he does not have to pay what he owes in child care. Is this true?

I am divorced single parent of two small children. I recently went back to work and needed to hire a nanny for the morning to prepare my children for school since I must leave for work much earlier than my children go to school. As per my divorce stipulation, my ex husband is to pay 67% of child care. My ex husband claims that a nanny does not meet the criteria for child care unless it authorized by government. I live in the NYC area. Is this true?