Little bear in trouble

'Why are you so fat?' little bear asks me, while I sort out stuff for him.
'Because I eat too much.' I say, as matter of fact as I can manage.
'My friend's mummy doesn't eat too much.' Little bear said thoughtfully.
'Thanks for that.'
'Mummy, you are ten metres fat.'
'Thank you very much,' I said flatly.
'No you're not,' little bear said, with absolute mischief in his eyes. 'You're twenty metres fat.'

He does like to push his luck. I did the only thing I could do - I gave him a severe, disciplinary tickle.