Recently, Maryland State Child Services made a "clarification" of the law in Maryland that says that a child under the age of 8 may not be left in public without someone at least 13 years of age to be responsible for them. Their "clarification" is that the law only applies when the children are within a structure, in other words when they are inside, and not when they are outside. I'll deal with all of the reasons that is a horrible way to interpret that law in my next post. This is to explain why the age of 8 was chosen. It may seem random and/or arbitrary but, in fact, it is not.
The brains of children under the age of eight have yet to develop the part that allows us to understand conditionals.
What is a conditional?
A conditional is applying any rule differently depending on the situation. In English language, it is an "if" clause. "If it is sunny out, we can go outside to paint." Adults intrinsically understand that that means that it if is not sunny out, they may not be able to go outside to paint. A child under eight does not automatically understand that. But it doesn't have to be stated as an "if" clause either.
A quick example from my work experience to illustrate:
When I worked in educational theater, we had a show in which the villain was a box of sugary cereal. The point of the show was to teach elementary school kids about making good eating choices by showing them what happens when a child chooses only high sugar foods and lacks nutrition. We were getting feedback from kindergarten teachers that their kids were going home and telling their parents that nobody should ever eat cereal because cereal is bad for you. In talking to the folks in our education department, they pointed out that kids this age cannot understand that the cereal is bad for them only IF it is high in sugar, if it is the only thing they eat, and if they are trying to start their day with it. They were not able to understand that the same cereal would be a perfectly good choice for a dessert after eating a balanced lunch or dinner or as a sometimes treat. They were not able to understand that a different cereal that is high in whole grains, contains a full serving of fruit and has little or no added sugar can be a good choice for breakfast. The classes who were eight and older did not have this issue.
So if a child is not able to understand conditionals, it also means that they do not possess the brain space to make decisions that require judgement. Children under eight cannot determine whether or not it is safe to cross the road if there are any cars on the road. Likewise, they cannot determine that if a car changes its path, it may require them to walk faster to get out of the road before the car reaches them. I realize that the driver is supposed to be watching where they are going and is supposed to not hit a person in the street in front of them. But we all know that too many adults are distracted while driving. Consequently, even adults get run over by cars with a degree of regularity.
A few other things a child under eight cannot do for themselves include:
determining whether or not they will be able to get down from a place they can climb to,
judging whether a stranger on the street is "safe" to interact with, and
judging the slipperiness of wet surfaces.
All of these things represent a danger to children under eight playing or walking outside without an older person in attendance.
To the people who aer going to cry "helicopter parenting!":
Just because you are there to help them when they need help does not mean you have to do everything for them. But if you aren't there when they need help, you can't help them.
This age restriction was not picked out of a hat. There is child development science behind it. And that's why children under eight shouldn't be left unattended anywhere.