But his other boys, Brooklyn, 12, and six-year-old Cruz have stayed loyal to their dad's old side.
Becks said: "I tried to get Manchester United shirts on them early.
"Two of them are Man United fans and one of them's an Arsenal fan. I don't know how it happened.
"Actually, I do know how it happened.
"I had that when I was a kid with Man United."
Becks, who plays for LA Galaxy, told Shortlist magazine: "I let them support whoever they want."
One-year-old daughter Harper has yet to decide.