Yup since DS was about 2. He was outside no word of exaggeration for almost 4 hours straight yesterday. Even had his lunch outside DH said. (only 13C temp too) He HAS to exist outdoors, so I cannot be there all the time. He is very reasonable and likes to follow rules, so that helps. We have a pool but it is in our ravine area of the garden and is fenced in with a lock. The rest of our property is not fenced or gated. He often goes to his grandparents (2 doors down) and our next door neighbours (eldery avid gardener couple, like 2nd grandparents to him) the only rule is he has to walk across the front garden not the street and he HAS to tell me when he is going there and he has to tell them when he is retuning home.
I keep the windows and our back door with screen open, so I can hear him from all parts of the house. I often check him and usually say "You ok?" We taught him last year he always has to answer when we call him no matter how busy he is, just a simple "I'm over here, or I am ok." he also cannot go to our neighbours when they are not out there or DH and I are not with him as they have a huge pond and that is a huge safety concern.
He is also not allowed to cross the street to visit friends and neighbours alone. He can ride his trike anywhere on the property out back but not the driveway when alone in case someone pulls in and doesn't see him. he can use the drive when I am out with him.
Does she have favourite things to do out there to stay busy? Nello usually digs, mud pies, builds radar stations (don't ask

) uses his sand box, diggers, tractors, slides, climbs, shoots hoops, rides his trike and car, plays with his bbq and as we speak he is using his toy chainsaw on some old tree stumps and piling the branches near our fire pit LOL! Lots of things to keep him busy. So, set up clear rules, keep her busy and keep checking/visiting on her.
HTH,
A x