With apologies to his future biology teacher (TMI sorry)

'Mummy, my poo comes from my willy doesn't it?'

'No darling, poo comes from your bottom. Wee comes from your willy.'

'Nooo Mummy, it comes from my willy! I want it to come from my willy.'

'Well it's not really up to Mummy, it's the way you're built. Everyone's poo comes from their bottom. Mummy doesn't even have a willy!'

(crying now) 'Nooooooooo MY poo comes from MY willy'

(noncommittal) 'OK darling'

Sometimes you have to know when to give up the argument.