What is a "trust" kid?
Do you mean trust fund kid? It is a kid who comes from a wealthy family who has set up a trust fund to pay for expenses. Often times, but not always, they become brats because they don't understand what it is to work for something.
You mean a Trust Fund Kid? It means a kid whose parents have set him up with money in a trust fund.
I'm assuming you mean trust fund kid. It's somebody who's parents have passed and have left the person a trust fund that pays out a certain amount of money.