a - stay home alone for an hour
It would be from around 5.00pm to 6.00pm once a week, whilst waiting for dad to get in from work.
b - be met at school by their 12yo cousin and walk into the town to get tea (5 minute walk), before taking themselves off to their dance class (a further 5 minute walk).
I would meet them there and they would be alone for around an hour. They have phones.
Again, this would be once a week.
I haven't done any of the above yet, but am seriously considering both.
In each incident, I would be a 10 minute drive away.
What would you say is old enough for a child to do these things?