As you can imagine, this can only happen when an individual regularly exercises. Typically, it's aerobic exercise that improves cardiovascular fitness - but, where children are concerned, we can't think of "aerobics" in the same way that we do for adults.

For one thing, children won't exercise for the same reason we adults do. Most adults exercise for the sake of their health or because they want to look good. Children should never be encouraged to exercise because it will make them look good, even if obesity is an issue. Emphasizing exercise for the sake of appearance places the wrong value on physical activity - and appearance!

As far as health benefits are concerned, unlike adults, young children live very much in the present moment. They're simply incapable of projecting themselves into the future. So you can't expect your toddler, preschooler, or even your first-or second- grader to exercise because it will ensure he's healthier at age 40 or he'll look and feel better at 60. Even if you explain that exercise will make him healthier right now, you're not likely to get an enthusiastic response. These are all adult concepts - adult goals - beyond a child's cognitive and emotional capabilities.

Additionally, young children are not made for long, uninterrupted periods of strenuous activity. So expecting them to jog, walk briskly, or follow an exercise video for 20 to 30 minutes, particularly before the age of six, is not only unrealistic but could be damaging. At the very least, it can ensure an intense dislike of physical activity that results in a lifelong devotion to being a couch potato. Rather, when we consider developmentally appropriate aerobic activities for children, we should be thinking along the lines of moderate to vigorous play and movement. Physical activity that's moderately intense will increase the heart rate and breathing somewhat, while vigorous-intensity movement takes a lot more effort and will result in a noticeable increase in breathing. The latter can usually be sustained for a maximum of 20 to 30 minutes.

Riding a bicycle, swimming, walking, marching, chasing bubbles, playing tag, dancing to moderate- to fast-paced music, and jumping rope all fall under the heading of moderate- to vigorous-intensity exercise for children. In other words, it's anything that keeps the child moving continuously, sometimes strenuously and sometimes less so.

The American Heart Association assures us we needn't be concerned with target heart rates in children. Yes, we want to get their hearts pumping on a daily basis; but, whenever possible, we want to ensure it happens naturally. If you've noticed your child is definitely not getting enough exercise to improve cardiovascular fitness, joining in on the play yourself may be all that's needed. Start slowly, gradually increasing the length of time you maintain movement (by a few minutes a week) and stopping immediately should your child experience any discomfort. Before you know it, daily or almost-daily, moderate- to vigorous-intensity activity will be a way of life.

Rae Pica is a children's movement specialist and author of Your Active Child: How to Promote Physical, Emotional, and Cognitive Development through Age-Appropriate Activity (McGraw-Hill, 2003). Rae speaks to parent and education groups throughout North America. Visit her and read more articles at www.movingandlearning.com.