First of all it is important to remember that bike helmets are safety equipment and not toys. Standards are put in place to help you in your choice and allow you to turn to reliable helmets in terms of security.
First of all it is a well-known physical phenomenon. Think of the stools, to stand up the minimum is 3 legs ... on 2 legs we fall. Also the 3-wheels scooter offers a natural balance, as on the bike with small wheels. When for a classic 2-wheels scooter you have to find the point of balance, with 3-wheels models your child can let go of the handlebars and the scooter stays upright.
In Dog Scooter safety goes by line of line attached directly to the bike. The dog leash adapter is a clever mix of flexibility, rigidity and safety.
The safety of children in scooter or bike riding should be a constant Priority.