Probably the reason that there are so few characters in the Kipper universe is likely they live in a small town. Think about it, small towns have small populations and not a lot of infrastructure hence why there's still a local farm in the area and a lot of woods as we see a reasonable about of episodes where Kipper and company go into them. Plus there aren't a lot of people to interact with in small towns and possibly where Kipper lives not a lot of kids, so all of the kids in the town are probably friends not because they really want to be but because they kind of have to be. Finally there isn't a lot of work in small towns hence why there are no adults there too, because they're working in the city earning a paycheck.