Rav Yizchak Zilbershtein, rav of Ramat Elchonon of Bnei Braq, was asked if a parent could buy an electric bike for his/her child, or if they could allow the child to ride one.

Rav Zilbershtein responded that there is nothing to consider, and based on the number and severity of accidents involving electric bicycles, they should be treated as an item that is dangerous to the public.

Parents that have allowed their children to use electric bikes should know that they are partners to actual murder (base don a gemara about parents being accessories to a crime for not preventing it) and will be considered as murderers and be made to pay for it.

A parent under pressure to buy such a bicycle should know that an electric bike is like a gun. Giving such a bike to a child is similar to giving the child a loaded gun.
source: Kikar