A child can generate an adult-sized claim
A collision between a bicycle and a pedestrian, or a scooter and an elderly person, can cause injuries measured in hundreds of thousands of dollars. The claim is made against the household, and personal liability on a homeowners policy is where it lands first.
Motorized versions may fall outside the policy
A pedal bicycle is generally covered under personal liability. An e-bike or e-scooter above certain speeds can be treated as a motor vehicle and excluded, which puts it in the same position as an unscheduled recreational vehicle. The distinction is technical and it decides whether there is any cover at all.
The umbrella covers the household, including children
Resident minors are included, which means one policy addresses every child in the house. That is the efficient answer compared with trying to raise the homeowners limit alone.