Fish and chips

Polling day so the primary was closed to younger lad, and exam time so older lad on 'study leave'. Result: the two of them at home all day and unable to go and see Thor because it's a 12A. So I tell them to meet me at work and then we all head across the road for tea: fish & chips, then sticky toffee pudding and banana split for them & coffee for me.

How is it a slight, not-particularly-tall 11-year-old can eat as much as his 5'11" solidly-built 15-year-old brother? Tardis-tummy, I presume.