Kids asking for the new craze of wanting their bike to sound like a real life motorbike and don't want to fork out for a piece of plastic like this link
for it to snap after 17 mins?
Get them a can of cola / lemonade on the cheap, shove it in their back or front wheel (don't do both or you'll cause an earthquake) and they'll have fun for hours! (We did)
[Please note other brands are available, prices are subject to inflation, once stock is gone that's it & T&C may apply - Note we cannot be held responsible for any damage caused by your children having fun]
If you really want to save money, use one from the recyclable bin that the council will refuse to take anyway because it's the wrong type of plastic or metal.....
PS You can also use plastic bottles but a slightly different sound..