To operate models on an AMA field you must either (1) be an AMA member, or (2) be a registered student in the Intro pilot program, or (3) be on a Buddy box with an AMA member.
This applies to Adults, Kids, Friends, and Neighbors. No AMA -- No operation of Cars, Trucks, Planes, or Helicopters at Higgins Field.
For Kids: Kids must be an AMA member to fly without a buddy box at Higgins Field. Fortunately, membership in AMA is FREE to kids, provided the proper paperwork has been completed and submitted. The paperwork can be downloaded from this link. All membership benefits begin on the day of receipt at AMA Headquarters of a properly completed application. Until this time a buddy box must be used with youth.
$2,500,000 Comprehensive General Liability Protection for model activities for members, clubs, site owners, and sponsors. This is why it's required.