Traveling with Children
International child abduction is taken seriously by both the United States and Europe, under the terms of the 1980 Hague Convention on the Civil Aspects of International Child Abduction.
Even when both parents are present, children traveling internationally may be questioned to ensure that they are actually traveling with their parents and live where the parents claim that they live. If both parents are not present, notarized permission to travel is always recommended.
Travel Consent Form
If you're traveling with children and their parents are not with you, prepare to be asked to provide documentation that you have permission to travel with the child. Ask the child's parent to sign a "Travel Consent Form," available free on many legal websites, and have it signed in the company of witnesses.
Attached is a sample travel consent form. Take the completed form along with you and have it handy when you fly.