Want to help your kids save money on their car insurance? You might want to consider keeping them on your family policy.

According to a new survey by insuranceQuotes.com, an 18-year old in Washington who buys an individual policy will pay, on average, about 28 percent more than if they continued on the family policy.

"And that's really just a huge incremental cost that they don't have to undergo," said Laura Adams, senior analyst at insuranceQuotes. "If they stay on mom and dad's plan, mom and dad are certainly going to pay more, but it's a heck of a lot less than the teen is going to pay on their own."

If you want to encourage your son or daughter to be financially independent, just have them pay for all or part of that premium increase.

"That makes everyone happy," Adams said. "Mom and dad are getting reimbursed and the teen is getting insurance at the lowest rate possible."

And of course, that extra cost will drop each year as your son or daughter gets older.

More Info:Should young drivers stay on their parents' auto policy or get their own?