Best Credit Score Trick For Kids

"It is this simple", says the father of 3 kids two of whom just bought their own cars with the best rate possible from the local credit union. Put the kids names on the most used household credit card that gets paid on time every month and has a decent credit limit.  Of course you DO NOT give a card to the kids nor do you even tell them that their names are on the card UNTIL you go with them to the credit union and they pull up their 765 credit score for an 18 year old.  
He measured the difference in paperwork in inches and the rate was just barely above free.  As far as he can tell it cost him nothing to get this done, the kids were 17 at the time, and the twins in the case are off to a great start with their own credit at the top of the rankings.  Way to go DAD!