Cyclists and other wheeled vehicles shoudn't be on sidewalks.   How many times have I been out walking when there aren't a lot of people around (and little traffic) and a cyclist comes from behind whizzing by without warning, coming within a couple of centimetres of hitting me.   

Whether or not they use a bell is irrelevant;  some people can't hear them.   It's super dangerous.  Ticket, ticket, ticket away.

As for little kids with scooters and so on -- that's fine within limits.   Some go too fast though and their parents should be ticketed when that happens.