Halloween costume competition prize?

[PyongyangKipperbang]

I need something about £20 suitable for a child aged between say....3 and 12 as a prize and my mind has gone blank! All I can think of is something art/crafty but that seems a bit crap.

any ideas?

That's a big age range. Amazon gift card?

Slime making kit.

Ooh slime make kit could be good!

I wanted to get a gift card but my boss wants an actual prize....