The throttle has self destructed. Where and how can I order/buy a new part?

My two step children were given a broken mini-moto bike by their Granny. The throttle is completely missing and I want to know were to get the parts to fix it! It's not a normal throttle set up for a bike is it? Or is there a proper dealer to go too? If any-one can give me an answer it would be much appreciated. Thank you