noun
child's ID tag; lost child tag
A tag attached to a child's clothing or belongings with their name and contact information, used to help reunite them with guardians if they get lost.
遠足のときは、子供の服に迷子札を付けてください。
Please attach an ID tag to your child's clothes for the field trip.
この迷子札には名前と電話番号が書いてある。
This lost child tag has a name and phone number written on it.
迷子 means a lost child; 迷子札 is the tag used to prevent or resolve such situations.
Compound of 迷子 (maigo, 'lost child') and 札 (fuda, 'tag, label').