Under 12 years old: must travel with a responsible person aged 16 or older.

12 to 15 years old (inclusive): can travel on their own, as long as they’ve got a fully completed Eurostar unaccompanied minor form. This must be signed by their parent or legal guardian (or by a responsible adult given consent by the parent or legal guardian) at the station in the presence of a member of the Eurostar team.
 
Children under 16 cannot travel unaccompanied on the direct route between London or Ashford and Lyon, Avignon and Marseille, Rotterdam, Amsterdam, on our direct ski trains to the French Alps and between Brussels and the Netherlands.

The child will need to keep this signed form with them throughout their journey and show it to the onboard team if they’re asked.
16 to 18 years old: can travel by themselves, as long as they’ve got all the usual travel documents and meet all the legal requirements (please see below).

French citizens and foreigners living in France
 
From 15 January 2017, anyone under 18 who is a French citizen or a foreigner living in France must complete an Authorisation des sortie de territoire (AST) form before they travel alone or without their parents.
 
This applies to journeys from France.
 
Documents your child will need

Up to 16 years old	Up to 18 years old
All unaccompanied minors Eurostar ticket Identity card or passport Eurostar unaccompanied minors form signed by parent   French citizen or a foreigner living in France who is leaving France: As above, plus: Authorisation des sortie de territoire (AST) form signed by parent Photocopy of the identity card or passport of the parent who has signed the AST form	All unaccompanied minors Eurostar ticket Identity card or passport        French citizen or a foreigner living in France who is leaving France: As above, plus: Authorisation des sortie de territoire (AST) form signed by parent Photocopy of the identity card or passport of the parent who has signed the AST form