What lock do you suggest for a kid’s BMX in Manchester?

My default would be an Abus Granit, Kryptonite New York or a Kryptonite Fahgeddaboutit with a curly cable or chain to keep it all together. But I reckon any of those would be too heavy and fussy for a 10 year old to tote about.

I guess something simple, light & easy to carry in a backpack, easy to use and yet more secure than a ‘regular’ lock.