The Office of the National Rail Safety Regulator calls them pedestrian conveyances.
Pedestrian conveyance. i.e., any human powered device by which a pedestrian may move other than by walking or by which a walking person may move another pedestrian (e.g., baby carriage, roller skates, skateboard and non-motorised scooters and wheelchairs);
The ICD 10 Category V00 for various pedestrian conveyance accidents is more specific, using the term rolling-type pedestrian conveyance in a breakdown of accident types. The conveyances listed by name at item V00.1 are in-line roller-skate, non-in-line roller-skate, skateboard, scooter (nonmotorized) and heelies. Other categories include gliding-type (V00.2) and flat-bottomed (V00.3) pedestrian conveyance accidents.
Note that push-bikes (non-motorised bicycles) are notorious for falling into a grey area as far as their legal status as a vehicle is concerned. This is dealt with as a special case, for example:
under the New York Vehicle and traffic law a bicycle is defined, statutorily, as a vehicle
Whether they (bicycles) are pedestrian conveyances is also questionable, as noted in the comments below. The following heading can be read either way, depending on the scope of the word "other":
Bicycles, skateboards, scooters, rollerblades and other ‘pedestrian conveyances’ are great fun for kids.
Consider the labels given by department stores (note: these links go to commercial sites):
- Walmart - Kids' Bikes & Riding Toys
- Target - scooters, skateboards & skates
- Toys R Us - Bikes, Scooters & Ride-Ons
The lack of a generic term in commercial sites suggests that there isn't a popular/slang label for this category of conveyances.