NEW YORK (CBSNewYork) – We typically think of heart disease as something that happens in old age, but in fact, it actually begins to develop in childhood.

That’s why it’s important to start cardiovascular prevention early in life.

How early? A new study says as young as three, four, or five years-old.

Kids playing outside as summer vacation hits across the U.S. – that’s what childhood is supposed to be like. Just running around and playing.

While many kids are having fun, believe it or not, they’re also doing something to help prevent heart disease.

“This kind of activity has been shown to preserve cardiovascular health in older children and adults, but it is not clear if this is true in young children,” Nicole Proudfoot of McMaster University said.

So that’s what researchers set out to show – that even in pre-school, moderate to vigorous physical activity works to prevent early heart disease.

The findings are in the July issue of the journal Pediatrics.

The Canadian researchers followed the physical activity of nearly 400 per-schoolers for three years, periodically testing them on various measures of cardiovascular health.

“Our finding showed that even during early childhood, physical activity is beneficial for blood vessel health and for cardiovascular fitness. Young children who were more active lasted longer on the treadmill test, indicating they had better cardiovascular fitness and there heart rates recovered faster after exercise,” Proudfoot said.

Even more significant, the researchers said these beneficial effects of physical activity may carry over into later childhood and even adulthood.

Dr. Kathryn McElheny, a sports medicine physician at the Hospital for Special Surgery says there are a couple of reasons that may be true.

“There are probably physiologic mechanisms that can potentially carry on to adult life. The more active you are as a kid, the more likely you are able to maintain those activity levels into adulthood,” McElheny explained.

Obviously, this means that young children should be encouraged to get away from their video game screens and go out and play.

For pre-schoolers, that means unstructured play, not organized sports or classes. Let them run around, play tag, climb the jungle gym.

Resist the urge to enroll them in formal sports until first grade or so, CBS2’s Dr. Max Gomez suggests.