2Pcs 150mm Steel Bicycle Rear Derailleur Protector - Durable Bike Derailleur Guard & Chain Stay Protector for Mountain & Road Cycling (Black) - Perfect for Off-Road Adventures & Commuting

These should be on every kids bike. When your kid drops their bike on its side it weakens and bends the delicate plastic derailleur that comes on budget kids bikes and leads to shifting problems.Doesn't come with screws because every bike is different but mine was M6. If you can't find one short enough that it won't interfere with gears then put a nut on the bolt before you screw it in which effectively shortens the threads.