Beckham, 41, and his wife Victoria, 42, have come under fire for allowing their youngest son - who is signed by Justin Bieber’s manager Scooter Braun - to enter the music scene.
Ex-footballer Beckham told Good Morning America that the track was a one-off and did not signal the launch of Cruz’s music career.
“We only realised that Cruz has a cute little voice about nine months ago,” he said.
“Scoots has been a family friend for a while. He said ‘bring him in, see if he enjoys it’....
“We always hope that our children listen to us..we do a lot of work for charity...and Cruz came to us and said: ‘How about I do a Christmas song for charity?’... There’s nothing more to this than that at the moment.”
Beckham told the US show: “He’s 11 years old, he’s still at school, he’s concentrating at school, that’s the most important thing. But he wanted to give back and he’s done this amazing little Christmas song which has got a lot of attention.”
Beckham, who was on Good Morning America to talk about his work as a Unicef goodwill ambassador, added: “We’re very proud of him. He came to us with the idea. It’s kind of cool, he’s having fun.”
Good Morning Britain host Piers Morgan attacked the Beckhams, calling them “shameless”, after news emerged that Cruz would be releasing the single.
“I say why don’t you go to school, mate, because you’re not famous, your parents are famous ... stop putting these kids into the public domain while simultaneously saying privacy,” he said.
The row came after it was announced that Brooklyn Beckham, the couple’s eldest son, is releasing a book of his photography.
Earlier this year, he was invited by Burberry to shoot its latest fragrance campaign - which photographers complained devalued their skills.
The Beckhams’ other son Romeo has also worked with Burberry - modelling clothes for the fashion giant.