Since leaving school, the aspiring model has found work on a building site - much to the amusement of his dad and older half-brother Lennon, 19.
Lennon - whose mother is Liam's first wife Patsy Kensit - said: "It was for a week."
Liam laughed in a joint interview with his children: "It was a couple of days, weren't it. It wasn't even a week!"
The 46-year-old rocker shot to fame as a member of Oasis alongside his brother Noel and with both his sons keen guitarists, Liam thinks they should start their own band together but the teenagers aren't so keen.
He said: "I think they should start a band together, but they don't want to. They want to do it themselves."
Lennon said: "If it happens, it happens, we're not ruling it out. Early days."
And Liam - who also has Molly, 21, with Lisa Moorish and Gemma, six, with Liza Ghorbani - admitted his kids aren't big fans of his music and would rather be "getting off their heads" backstage with his girlfriend and manager, Debbie Gwyther, than watching him perform.
Lennon said: "You've got a few good songs."
Liam admitted: "I don't think they're big fans of Oasis. I mean, they come to my gigs, but you can see they're just going, like [yawning], 'He's doing 'Wonderwall', that's got to be near the end.' Or you look round for them and none of them are there -- not even Debbie. They're all backstage, getting off their heads."
- BANG Showbiz