meself - I call it pre-after school care because we drop the kids off there before school begins and pick them up after school ends. They are then taken to school in supervised groups.
School hours are 9am to 3pm. So I drop them off, around 8-830 and my wife picks them up around 5;30. (At after school care they have various activities, crafts, games or playing in the playground, during the school year - the after school care is available during holidays as well as the summer break - for a fee of course) I should also add that breakfast is included though we have our breakfast at home during which time we read to them.
The alternative would be for them to walk home and be alone until we get home.
As far as I know the law in Canada (where we live) there is no specific age as to what age is ok to leave kids alone. It really depends on the maturity of the child and parents must ensure that kids are not in danger (if it can be determined by police that children should not have been left alone - then they could be charged with child abandonment - this from Safe Kids org
Obviously the key is what is reasonable, and understanding the maturity of your kids and what they can do.
Still, I recall my brother and I were latchkey kids and were alone unsupervised. I also cringe at some of the stupid things we did as kids, ie. playing with fire, throwing knives up in the air. (among other things) that we never told our parents about.
On the opposite end of the spectrum, I just watched a film on netflix (Maidentrip) about Laura Drekker a 16 year old Dutch girl who sailed solo around the world - part of the story involved a fight with Dutch authorities trying to prevent it (by taking custody from the father).