There's the other extreme where negligent parents do not take
enough care of their kids, resulting in nasty injuries or worse,
death. 
I think before a kid turns five, the parents need to keep a close
watch on them. The younger they are, the more vigilance is
required. And then, once the parents have inculcated a logical
sense of safety in the kids, and once the kids have proven to have
a level of street-smartness about them, they can gradually earn
more and more freedom.
Recently, a toddler was found hung by his mom because he had
climbed to the top of the washing machine and tried to get out a
window, but slipped and his bike helmut was caught in between the
window and the wall and he was hung by the strap of the helmut.
His twin brother
is still too young to fully comprehend why he's no longer around to
play with him.
Kids also need to learn about stuff like snakes, centipedes, etc
before being allowed to roam free. Look through books / websites
with photos of dangerous / poisonous insects / reptiles / animals
with them before letting them explore the bushland.
Safety first.
