[Albion Wilde]

Hot food takeaways would also be barred from opening within 400 metres of schools

That's a quarter of a mile, about 4 city blocks—not much of a challenge for teenagers.

[Winniesboy]

That's a quarter of a mile, about 4 city blocks—not much of a challenge for teenagers.

For a 'normal' teenager, yes. But for a teenager of the size being targeted by this, 400 metres presumably looks like a double marathon.