Well my maim concern with kids going out is traffic, so I am very hot on road safety.
But by not allowing them any freedom before high school how do you think they will magically then be safe to go out on their own at high school age?
What is the difference in a yr 6 child in June to the same child who is at high school in the Sept? Unless you teach them and give them opportunities to learn there is no difference.
Yes it defends where you live, one of our parks is by woodland and marshes so they need to know where they can go to play, ds2 can go there on his own and ds3 will be allowed this summer, they will stick to the park and the hilly area away from the marshes. If they want to go in that bit I would-be at the park with them. But they can go over to the park on their own, and I will meet them later or if we are at the park together the elder ones can go home on their own and I join them later with the little ones. Children of 9/10 etc can be quite capable given the opportunity and ime it's good for them to do stuff. Ds3(9) enjoyed going round the garage sale on his own today, we started off together, then he went off for a bit, then we met up again and then he walked home on his own whilst I took the little two to the shop. Ds1(14) and ds2(12) stayed home on their own.
We are lucky we live in a nice area for kids with shops, park, library etc all close enough for them to be given age appropriate freedoms.
My high school kids have a fifteen min walk to the bus stop and then catch a public bus to school, the freedoms that I allowed them at 9/10 etc helped prepare them to be able to do that journey on their own.
You know the area you live in, but generally by high school age (if not before in many countries) children will be going to and from school on their own and meeting up with friends out if school, it seems madness to not allow any freedom at all until high school age and then when they are going through the upheaval of starting high school and all the changes that brings to suddenly expect them to cope with other responsibility and freedoms. Far better ime to build up gradually.