opriate risk-taking. Fear of litigation results in minimising "risk" at all cost and decreasing the value of "real play" that occurs on school playgrounds [2, 3]. Several schools have now placed a ban on running on the school playground [4, 5]. Thus, "surplus safety" may result in exactly the negative outcomes it was meant to avert . Although no research has directly examined risk avoidance and children's health outcomes, recent Australian data suggest that concern with children's risk exposure can lead to constraints on children's habitual physical activity, which may have negative public health outcomes . Further, when children perceive that play settings are not demanding enough, they may compensate by engaging in activities that yield challenges -- in the context of undesirable behaviour (e.g., bullying or using play equipment in truly dangerous ways).
Social and Physical Environments Affect Play
Opportunities to engage in spontaneous play in the local neighbourhood have declined in recent generations . The age at which children are allowed outside to play on their own has increased in recent years . While parents of older children may have greater tolerance for allowing their children to take manageable risks, young children are generally not allowed to engage in what parents perceive as risky play or activities. Mullins and colleagues  speculated that parents are less likely to engage in overt overprotective behaviours as their children reach adolescence, yet still perceive their child as vulnerable. Children are often driven by car to play activities  and these activities are likely to be adult-organised and indoors . When children are allowed to play outside, it is often on the school playground for which rules limit play behaviours  and purpose-built equipment (e.g., slide) fails to promote collaborative and imaginative play. Slides and climbers are also the source of most serious playground injuries  and climbers are often places in which less physically competent children are teased by peers .
In contrast, natural play spaces (e.g., woods, gardens) and playgrounds with unstructured construction materials stimulate diverse and creative play . Fantasy and socialisation are prominent and the social hierarchy is based on the ability to imagine what the space might become rather than on physical prowess . Children experience active play through lifting, pushing, and pulling. They engage in creative, socially interactive play as they construct new structures and play within them . Both in our pilot study [20, 21], and in a study at another Australian school where children played with unstructured materials, reports of injuries, bullying and fighting were almost non-existent .
Sedentary lifestyle and obesity
In Australia over 200,000 children are obese . Childhood obesity is a serious problem with a range of significant medical, psychosocial and economic consequences . Despite the growing awareness of the consequences, the prevalence of childhood overweight and obesity is still high in many westernised and westernising countries [24, 25]. Regular physical activity is associated with both a longer and healthier life , including a decreased risk of obesity , insulin resistance  and metabolic risk . Similarly, physical inactivity during the early years of life is a major contributor to serious medical conditions in children [30, 31]. Time spent participating in sedentary and low energy-expending activities is associated with higher relative weight [32–34] and poorer health. Hence, a reduction in sedentary behaviour is important for promoting health .
Several underlying issues may contribute to the increasingly sedentary lifestyles of some children. In many cases children are reliant on parents when it comes to the activities they undertake. Families live exceedingly busy lives with limited time for children's free play and unstructured activity. To "make the most" of the time they have, many middle-class parents enrol children in organised activity and sport [36, 37] that offer strictly scheduled, structured exercise an