New York Mobile Notary Service offers Emergency Airline Notarization for "One Parent - Minor Child" boarding denial situations. Many airlines require the Notarized permission of the Child's other parent for you to board the plane. This requirement is to help protect the child from "kidnapping" by a parent or other individual. Keep in mind that the airline is protecting the child.
Next, contact the other spouse. Explain the situation. They will have to travel to the Notary's location, WITH their driver's license or passport as identification. Also required will be the name of the child and the flight information and destination.