How old are the kids?

When minors travel without either or both parents, some jurisdictions require a (notarized) statement that they have the parents' permission to travel. It's also wise to give a medical power of attorney so that emergency health care can be authorized. The extent to which this matters depends on the laws of the destination country as well as those of any transit points.

I would expect increased attention to minors traveling without parents due to recent publicity regarding trafficking of children.