|Laker fans Will Ferrell and and his son Magnus Ferrell at Staple Center.|
He told 'Late Show' host David Letterman: "The two year old unfortunately is just wandering into vulgarity - he has two big brothers, it wasn't from me.
"I'm trying to prevent it. I'm doing everything humanly possible. I'm having a good laugh and it's out of my hands, I can't control it.
"He thinks it's hilarious - and so do his brothers - to walk up to anyone, male or female, and say, 'You have a little penis.' He'll get on a roll and say it over and over again."
Will is even planning to use the youngster's love of the insult to play a joke on some showbiz pals.
He explained: "My brother-in-law wants me to have a big Hollywood party and invite loads of actors, then hopefully he'll walk up to a George Clooney type and say 'You have a little penis'. He thinks it would be really funny."
Meanwhile, Will revealed his 'The Campaign' co-star Zach Galifianakis gave him a generous gift for his recent 45th birthday.
The 'Hangover' actor presented his pal with a cheque for $5 million - but then was told to "wait to cash it".
Will added: "There might be a hold on it."