Button

Diesel - "Mummy can I be button again"
Mummy - "Ok night night Button"
Diesel - "No not here I want to be in your tummy again"
Mummy - "You can't, look how big you are, you won't fit in my tummy anymore"
Diesel - "Oh, can I be a taxi driver and a digger driver instead then"

Older

Mummy - "What do you want to be when your older?"
Diesel - "A fireman or a dinosaur"