According to an article in the December 2004 Journal of Sports
Medicine and Physical Fitness, playing children's games can help
adults get their recommended amounts of daily physical activity.

In one study, researchers looked at the role of family interaction
and physical activity. The 20 adults in the study played soccer
and nerf ball one-on-one with 20 children. For five minutes per
game, researchers measured the adults' heart rate and expired air
and calculated metabolic equivalents (METs) and number of calories
burned. When the adults played with the children, their average
heart rate was 88% of max, they averaged about 6 METs, and they
burned about 40 calories.

The researchers concluded that adults could reach their recommended
levels of physical activity by playing these games with their kids
for about 20 minutes.