Having played computer games for 20 years of my life, I often hear that it is wasted time.
First of all. Time spent fun is never wasted. You only live once and every second you are happy is the best of time investment considering we are all going to die anyway in my opinion.
That was just my opening argument, which I feel is in itself good enough to justify it. But here is the real deal:
Language skills. I had a D in English until gaming really took off as a hobby, I went from a D in oral+written exams to a B written (I still suck at grammar in all languages, so a B for me was a very strong grade) and straight A's in my oral exams. Note: Im not a native English speaker.
Team work. Playing MMO's taught me to cooperate and work better with other people.
Cultural. Playing MMO's taught me alot about other people's culture and countries, having played with russians, koreans, arabs and so on. Through voice chat and ingame conversations I learned alot about other cultures and countries and got a real life perspective and information about them.
Personal development. Many games, RPGs in particular, has very deep storylines and teaches you diplomacy skills that can be applied to real life. They also have alot of morally ambigious quests, conversation and storylines that helps further critical thinking and so much more. Overcomming shyness is also something I can thank gaming for - as the need for voicechat and communication was vital to succeed.
So before you teach your children that gaming is bad. Consider the tonns of real life applications and personal development it contributes. Media does a horrible unscientific job of portraing gaming in the most negative way possible. I can say for a fact from personal experience built up over 20+ years, that it has left me with more knowledge, skill and personal development than it gets credit for. And Im positive that if real research was done about gaming and how it affects a person, the pros would far outweight the cons. That is ofcourse if the person does other things than just play as the dosage makes the poison.