Do not blindly give your child everything they request. Parents are obligated to feed, clothe, shelter and care for a child and young adult. Parents are not obligated to give children fancy toys, brand name clothes or every activity requested. By giving the child most of their requests, regardless of cost, the child comes to see these things as an entitlement. With age, the requests grow in cost. Instead of a day at the racetrack or bumper cars, the teen requests and expects a car. Instead of karate lessons and sports fees in the hundreds of dollars, it is a demand for a Spring Break trip in the thousands of dollars.
The first thing to do as a parent is rein in the "gimmies" at an early age.
If you are dealing with an teenager, whip out your budget. Show them where the money goes, including their expenses. Set a budget and help your teen budget for his/her own activities.
And teach them about work. How much do you make if it is minimum wage? What is left after taxes? If you buy this, you'd have to work X hours at Sonic or McDonalds to own it.