This can be a sign of shyness or anxiety. If it occurs at the beginning of a session, you can say, 'I realise it's hard for you to talk. This often happens to people who come for the first time.'
If the client is shy, you can legitimise the feeling by saying, 'I'd feel the same way in your place. I understand that it's not easy to talk to a person you've just met.'
If the young person has difficulty expressing their feelings or ideas, you can use some brochures or posters to encourage discussion or refer to a story so that they can talk about others rather than themselves.
If the young person cannot or will not talk, you should propose another meeting.