What is the legal age to leave children overnight for one or more nights with out adult supervision. I thought anyone under 18 was considered an "infant" in the eyes of a court. My ex sister in law is taking 2 of her children to Hawaii and leaving the oldest 17 to care for the youngest 11. She leaves them all unattended at times anyway as she is a flight attendant and thinks there is nothing wrong with it. This is in Washington State. Their Father and the rest of our family is all on the east coast and we never know when they are alone. This is the only time she has been so bold as to announce anyone would be left alone but we do not have any exact dates.