Kids. They grow up so fast.

These days, they don't just talk, act, and behave in ways far beyond their years-- they also face some of the same disease risks once seen only in adults.

Now, even tots barely out of kindergarten are showing some of the earliest signs of heart disease--and a new study links it to too much time in front of the TV.

Researchers in Australia quizzed the parents of 1,492 children between the ages 6 and 7 on how much time the little ones spent running around and how much they spent zoning out in front of the tube or plugged into their computers.

On average, kids spent nearly two hours each day as couch potatoes... and just 36 minutes a day playing outside and being active.

That's nearly 14 hours a week wasted in front of the tube... and just 4 hours and 12 minutes a week doing what kids used to do all day long.

And it's killing them.

You can't see the damage at the age of 6 or 7, not from the outside anyway. So the researchers photographed the arteries in the back of each child's eyes.

Why there? It's the easiest way to see the small arteries--and the widths of these arteries are often used to help predict heart risk.

The researchers found that kids who spent the most time being physically active had arteries that were an average of 2.2 microns wider than those of the kids who watched the most television.

And overall, the researchers say every hour of TV led to an average narrowing of 1.53 microns.

In adults, that's enough to raise systolic blood pressure by 10 mmHg.

Heart risk isn't the only problem associated with too much TV. One recent study of kids between third and eighth grade found that some children were actually TV addicts--watching 30 hours or more each week.

These kids were more likely to suffer from anxiety, depression, anxiousness and impulsive behavior. They were also likely to have problems fitting in with other kids and serious issues with their schoolwork. (Read more here.)

But all's not lost. If nothing else, kids have the advantage of time: They're young, and it's not too late to turn off the TV and get them out, active, and back on track.

Just don't wait too long--because they won't be kids forever.