For 17 year-old Mbabu - who can play at centre-back or right-back - the challenge starts here.
He said: "I've always wanted to play for a big club and I have my chance with Newcastle United.
"I'm delighted by the move.
"I want to finish my development here and then try to join the first team.
"The speed and pace in this country is at another level.
"I know I will have to work hard to achieve the level here because there are some top players here.
"But I already feel at home and the club have made me feel very welcome here already."