d play. In families with fewer financial resources, children are more likely to spend more time in front of the television instead . To make sure children's school results do not suffer, there is an increased emphasis on academic tasks, particularly in middle and upper class families. This increased pressure on children, in combination with the perception that there are many "predators" in public spaces, ensures an increase in screen- and homework time and a decrease in time spent outdoors. To save time and keep children "safe," many parents drive them to school and sport--creating a self perpetuating cycle.
Mental ill health and bullying
About 14% of Australian children have significant mental health problems . In children from disadvantaged backgrounds, this figure can rise up to 60% . Play is one of the best ways for children to develop coping skills, and thereby mental health. Play engages children's intrinsic motivation and supports autonomy, competence and relatedness that have been shown to promote psychological wellbeing .
Poor social skills have been linked both to bullying and being bullied  and children with higher self-concept are bullied less often and also are actively included in play more often [42, 43]. Our conjecture is that unstructured materials on the playground will give children who are not very sporty or physically coordinated the chance to play. Teachers participating in our pilot study reported that the unstructured materials promoted play between children who had not played together previously--including children who had formerly been excluded .
Play as an alternative intervention
Play is a universal and profound process that has evolved in both animals and humans. It is spontaneous, exploratory and intrinsically motivated . Children love to explore and delight in opportunities to devise their own free play to experience sheer joy and pleasure in the moment . There are many documented benefits to play  and this study aims to engage children's playful nature to promote greater physical activity and to enhance social skill development. When children play freely with materials that are intriguing and that also require physical exertion, we believe that they will spend more time engaging in the activity and thus also be more active for longer periods of time. When materials are large, a little unwieldy, or a bit heavy, it is possible that, in addition to expending more energy, and exerting greater effort, they will recruit help from other children, thus promoting social negotiation in the context of creative play (i.e., what can we do with these materials?). Play also offers opportunities for children to take manageable risks and to experience the benefits of a variety of challenges (e.g., motor, social, emotional and cognitive). The playground based intervention presented here is aimed at appealing to children's inherent will to play, rather than imposing a structured program or regimen.
Prevention strategies that target the population as a whole, rather than focussing only on children at risk are preferable. It is difficult to identify who is at risk and all children benefit from increased activity independent of body composition and interest . Thus programs conducted at schools can be highly beneficial.
Previous studies have supported play and changes to the playground as a way of increasing activity. In the UK, painting lines on the playground to promote active games resulted in small but significant and lasting increases in children's physical activity [49–51]. Placing play equipment and activity cards on school playgrounds in Belgium significantly increased the children's moderate to vigorous physical activity (MVPA) . Similar results were found in North Carolina where portable play equipment, including skipping ropes and hula hoops, at day care facilities increased physical activity . Turning a Canadian school playground into a natural play space also increased physical activity significantly . The same group of researchers also found that a higher percentage of children were engaged in MVPA