7 year old: 'Who's the biggest person in the world?'
5 year old: 'Mummy'
7 year old: 'She's not the biggest person in the world, she's the oldest'
5 year old: 'Oh yeah she's the oldest.' Pause. 'And her head definitely isn't the biggest.'
7 year old: 'Her head's tiny'
5 year old: 'Tiny. Like a pea. Pea-head'
[They dissolve into a fit of giggles] 'Mummy is a pea-head! Mummy is a pea-head!'
7 year old: 'But she's definitely the oldest isn't she?'
5 year old 'Yeah'
7 year old 'Yeah'
3 year old 'Yeah. Pea-head'.