Most accidents happen in the home. Most people do a poor job of making their home safe for infants. (EG look at the number of people in the UK who buy socket covers but who don't bolt their TVs to the wall)
Perhaps I misunderstand what you mean by "leave a 5 year old unsupervised" - does this mean "parent in the home but in different room"? Or "parent pops out to the local shop for half an hour"?
Because five year old children are far too young to be left unsupervised for anything over short lengths of time, and if a parent is regularly doing that they probably need a chat from child protection social services.