I would discourage the use of tricycles for children today. Training wheels are also obsolete. Kids should be started on a strider and go direct to two wheels. They develop a superior sense of balance this way and learn how to use their body to balance, it's better for their development and far more fun. However, tricycles are cool in a historical kind of way and that looks interesting, it would be good for a child with balance issues. My friend's kid was riding "skinnies" and a teeter totter on a pedal bike before he was 4. The C&V crowd might not know what that is, but these terms originate on the "North Shore" which is in North Vancouver, British Columbia and is perhaps the most influential area for mountain biking as it is today.