For family friendly dining options in Hong Kong:

Ruby Tuesday provides kids' menu, crayons, and balloons for the kids. High chairs are available. Quite pricey, and serves american portions.

Dan Ryan's also serve kids menu, and provides highchairs, balloons and sometimes free dessert for the kids. Seats may be a little cramped and timeslots may be in force.  During the holidays, Dan Ryan's decorate their restaurants quite well.  This includes Halloween (October) and Valentines Day (February) and makes meal times quite enjoyable for children. 

McDonalds, and KFC's are also all around Hong Kong, always a favorite among children.

Most major Chinese restaurants will have highchairs for kids. Japanese restaurants, ask for tatami rooms.

For a REALLY magical time with Disney Characters appearance, the buffet lunch at Disneyland Hotel is an absolute must try for families with kids, or anyone who is a fan of the Disney Characters. The buffet is beautiful, international cuisine of very good quality, and huge variety. Kids get highchairs, special Mickey Mouse plate, mug, fork and spoon to use. You might even forget you are in Hong Kong!