""However, parents commit an offence if leaving the child at home alone puts him or her at risk.""
That is often the criteria that the Police/SS use to decide if action should be taken. That and the reason why the child was left/used as a Babysitter.
My DD could be left at 12, with her equally sensible friend, minding my 10 year old. My Mum lived minuets away and I had really good Neighbours, which makes a difference.
My DD was working in a Nursery, on day and a half, release from School at 14 and was doing private Babysitting from that age.
When I was growing up in the 70's, a group of us would be left in the 'care' of two Teenage Sisters, both still in school. As said, young Women could live on their own with their Babies, at 16, up until recently. My Mum's generation went to work at 14 and ran the household when their Mother was unavailable.
So there should be leeway for discretion.
However I disagree with the opinion often given on here that toddlers can be left sleeping in Cars, whilst school pick-up is done, or in bed whilst the Mum goes to a local shop.