Stronglight also makes a decent crank in "kids" sizes, 155mm and shorter. STRONGLIGHT Impact Kid Chainset | £69.00 | Drivetrain | Chainsets | Spa Cycles
You can also just get the arms (and proper bottom bracket) and possibly use your current chainrings. STRONGLIGHT Impact Kid Cranks (pair) | £38.00 | Drivetrain | Chainsets | Spa Cycles They ship to the USA if you can't find a seller here.