Street or sidewalk?
According to the Highway Safety Code, it's forbidden to ride on the sidewalks which are intended for pedestrians only. However, it is common practice for children to ride their bikes on the sidewalk. As long as they are riding at a reasonable speed (5-10 km/h), children 10 and under can usually ride on the sidewalk. Children 5 and under should avoid the streets and limit themselves to the alleyways, the parks and the sidewalks. Children 6-10 can also ride in bike paths and in quiet streets, if they have a good control of their bike.
How to make rides fun?
Being a child may be a distant memory for adults, but you're probably well aware that fun and games drive their motivation. To make the ride more enjoyable, set fun goals to reach such as going to the park, getting ice cream or visiting a friend.
Adjust the ride to the child's level of profienciency and gradually lengthen it. The longer the trip, the more surprise snacks you should plan for!