Random Conversations with the Boy - continued

The boy is in that delightful "all bum jokes are hilarious" stage.
So today he said the word "ass" and fell about laughing. Of course I should have adopted my best serious mummy face and told him off but the context was very very funny.
My niece was commenting to my sister that she loved her handbag as it was really cool and trendy.
I mocked offence and asked my niece "Are you trying to say you don't just love my huge big red..."
(I was going to finish this sentence with "changing bag")
Which is exactly when J butted in ('scuse the pun) with "ass"?"
We did of course tell him that was not acceptable language and he asked why.
My sister replied: "Because it just isn't J. It's bad enough when you say bum or butt, never mind ass."
The boy looked at us, a wicked glint in his eye and proceded to sing
"Bums and Butts and asses, oh my..."

I didn't know whether to ground him or sign him for the Edinburgh Fringe.