From the GTSS Two-deep leadership:
Two registered adult leaders, or one registered adult and a parent of a participating Scout, one of whom must be at least 21 years of age or older, are required for all trips or outings. There are a few instances, such as patrol activities, when no adult leadership is required. Coed overnight activities require male and female adult leaders, both of whom must be 21 years of age or older, and one of whom must be a registered member of the BSA.
This can be found at www.scouting.org search for Guide to safe