Kai, 11, was pictured alongside his dad and mum Coleen putting pen to paper on a contract at the Old Trafford club.
Wayne – who played for United from 2004 until 2017 – wrote on Instagram: “Proud day. Kai signing for Man Utd. Keep up the hard work son.”
Kai was also pictured holding up a United shirt with the number 10 on the back – the same number his dad wore.
Former England international Wayne is United’s all-time leading scorer with 253 goals from 559 appearances.
