Canadian children are less active with age, according to the 1995 Physical Activity Monitor conducted by the Canadian Fitness and Lifestyle Research Institute. Whereas young children aged 1 to 4 spend almost 23 hours each week engaged in different kinds of physically active play, grade-school kids and teenagers spend about only 14 hours. What's more, teenage boys spend almost six hours more each week than teenage girls on physical activity.

Half of preschoolers participate in three major activities — running and kicking games, swimming (including things like Tots and Parents' swim classes), and biking. One-quarter participate in gymnastics and other movement games and in skating. Although they spend less time on physical activity, older children and teenagers participate in a broader range of activities, including many more sports.

Biking, swimming, skating and walking top the list of popular activities among 5-12 year-olds. Many more boys than girls participate in activities such as baseball, soccer, basketball and hockey. On the other hand, girls outnumber boys in gymnastics and in ballet and dance classes.

Among 13-17 year-olds, girls' participation rates are generally lower than boys', especially in more vigorous activities and sports. Biking, swimming, walking and skating remain at the top of the list for girls, but the top activity choices change for boys. Basketball replaces swimming as boys' second most popular choice and swimming drops to fourth place. Teenage girls' participation in physical activities generally drops after childhood, except in volleyball, social dance and basketball — all of which show a rise in popularity compared with early school years.

Childhood and adolescence are prime times for developing the skills and habits necessary for lifelong physical activity. Children should engage in frequent activity sessions each day, alternating bouts of activity with rest periods as needed. To derive additional aerobic benefits, adolescents should also engage in three or more sessions per week of activities that last 20 minutes or more and that require moderate-to-vigorous levels of exertion.