In Alberta, all children under the age of 18 are required to wear a properly fitting bike helmet at all times while riding their own bike or on or attached to an adult's bike (including in bike trailers). You will not be allowed to ride in a course if you forget your helmet, if it's broken or doesn't fit you properly. 

The government of Manitoba, together with CAN-BIKE Instructors, made this fun video explaining how to tell if a helmet is the right one for cycling and how to make it fit you:
There are many different looking helmets, but only a few types: there's helmets that are only meant for biking, or only meant for winter sports (skiing/snowboarding, ice skating, tobogganing) and some that are meant for more than one "summer" activity (skateboarding, inline skating, biking). Any helmet - even the wrong kind - is better than no helmet if you hit your head, but please check your helmet to make sure it's the right kind for biking. 
kids biking
Some studies have found evidence that wearing a helmet increases risk-taking behaviour, like riding faster or closer to autos, and that motorists seem to give cyclists without helmets more space. Overall, cycling is a low-risk activity, even accounting for the "extra" risk of wearing a helmet. But accidents do happen, and all people make mistakes: you don't want to find yourself seriously injured or killed because something happened and you hit your head. Helmets won't save you from everything, but it's the only thing we can do that provides some protection so wearing a helmet every time makes the most sense. 
Find your helmet boring or uninteresting? Consider covering it with a Tail Wags Helmet Cover! Available in over 40 designs, made in Canada and guaranteed to fit over any kind of sport helmet, there's a Tail Wags cover for nearly every person. To see what covers I have in stock or order direct from the manufacturer through my Affiliate link, follow this link.
Tail Wags