Interestingly, from my experience, those kids ride-on vehicles tend to contain what look like drill motors, geared down with a plastic gearbox. I took apart an electric ride-on 'motorbike' from when I was a kid, and that had two motors, run at 24v from two lead-acid batteries. Admittedly that'd be from about 15 years ago now, but I wouldn't have expected the design to change much. Whether they're drill motors just over-volted, or actually 24v motors, I don't know.