Here’s a great article I found on Summer Nanny (a website that assists nannies in finding summer nanny jobs):
The influx of electronic entertainment that seems to be taking over the modern household paired with unprecedented levels of parental fear have created a generation of kids that spend far less time enjoying the great outdoors than their predecessors. The resultant sedentary lifestyle that’s become the norm for many kids can lead to childhood obesity and related health risks, including diabetes and high blood pressure. What’s a parent to do when they’re not sure how much time outside is enough? This handy guide will help you get a basic idea of how much time your child should be spending outside and what her body needs to grow and stay in good shape, all while maintaining her safety and security.
According to research cited by KidsHealth.org, toddlers between the ages of 12 and 36 months of age should be spending at least 30 minutes of their day engaging in structured, adult led physical activity and a full hour of unstructured play each day. It’s also advised that a toddler never spend more than an hour at a time being inactive unless they’re sleeping. When the weather permits, spending your 30 minutes of structured play outside is wise, since kids so young probably shouldn’t be outside unsupervised. Just be sure that you apply sunscreen liberally before heading out the door, because toddlers’ sensitive skin can burn quickly. If you’re heading out for a day at the park, try to head home before your little one becomes so exhausted that she’s miserable and cranky.
By the time your child reaches the preschooler stage, between three and five years of age, she’s ready for a bit more independence. As long as they’re being supervised and are adequately protected with sunscreen, kids can spend a few hours at a time enjoying the great outdoors. Just be sure that they’re not outside during the peak hours of heat during the summer months, typically between eleven and two in the afternoon. If your yard is fenced or secure, be sure that they know not to wander away when your back is turned. At this age, it’s still wise to spend most of their outdoor time with them to ensure that they’re safe and not engaging in overly risky behavior. During colder months, KidsHealth.org experts state that there is no automatic cutoff time related to how long kids can stay outdoors, but that they should come in when they’re feeling uncomfortable and the weather feels unpleasant to them to avoid dangerous overexposure.
When your child reaches the early elementary years and above, she’ll probably want to spend time outdoors playing without direct supervision. Unless you live in a very secure area with a fenced property, you may want to work out a structured program in order to keep her safe. Kids should be allowed to come inside to warm up or cool down as needed, for regular rehydration breaks and to have snacks, as vigorous outdoor activity burns calories and dehydrates an active little body. The level of direct supervision that’s required is totally dependent upon the area in which you live and the type of security features on your property. If there’s a pool, trampoline or other attractive hazard on your property, it’s always best to keep a close eye on your children at all times when they’re outside. The American Academy of Pediatrics recommends that kids also have at least one hour each day to relax and enjoy unstructured, creative play time. Make sure that you allow enough time for your child to spend her hour in free, indoor creative play that’s not physically strenuous. The Mayo clinic also recommends that kids spend at least 30 minutes to one hour of their day engaged in active play, but that the prescribed hour can be broken down into 10 minute intervals when busy schedules don’t allow for a full, uninterrupted hour of play.