My daughter’s ex-husband has decided that it is safe to take my granddaughter (who is just five) on the back of his motorcycle. He has parental responsibility and there is no prescribed lower age limit (which staggers me), but I cannot believe she has the strength or concentration to hold on safely. It wasn’t clear if he has actually taken your granddaughter on the motorbike yet or “just” threatened it. As it seems both your daughter and her ex have parental responsibility (are there any court orders? These are usually used if parents can’t agree on how to exercise their joint parental responsibility, for example, with regard to schooling or medical treatment, but they can also be used here.