"Young Eagles and EAA’s New Youth Protection Policy
"This short document is intended to help you understand how Young Eagles is impacted (or not impacted) by the new policy at EAA....
"The only waiver necessary for a YE rally or flight is the standard YE form, which is sent back to Oshkosh after the flight. Chapters have no responsibility to retain any records from YE activities. Parents also do not need to receive any more information than the regular YE flight registration. Further, there is no need for a sign-in sheet for YE rallies."
Can't find the quote right now, but no, you can fly 3 kids in a 4-place aircraft. No need to take another adult along.