A minor is a child under a certain age. The relevant age varies depending on whether you are talking about SCA corpora, kingdom law or mundane law.
In the SCA jargon of many regions a minor child is typically referred to as a small and teenaged minors as teens.
There are restrictions in the SCA on what age a minor can train or authorise in combat-related activities, and there are often separate forms for membership, etc.
One form of activity for minors that has developed recently is boffer combat, armoured combat using hollow plastic tubing wrapped in foam for weaponry. Boffer has become increasingly popular in the Kingdom of Ealdormere over the past several years.