I'll just give the definition of rich, middle class and poor kid.
Rich kid: A kid who gets everything they want, their parents have good jobs, has a
good life and has a lot of expensive things. Their parents generally fall into the upper middle class/lower upper class or the upper class.
Middle class kid: A kid who has some things, their parents have decent jobs, they
have a good life and has a lot of average priced things.
Poor kid: A kid who doesn't have a lot, their parents may have a low paying job or no job, they have a decent life and doesn't have very much.