My youngest son is the youngest kid in my area. He's 11. None of my children, at any age, would have even dreamed of going into a neighbors yard without permission, from the neighbor, and myself.
There's no real fences around here either. My next door neighbor has a wooden fence, that anyone could walk right through, because her dog trends to run away, but honestly, my kids would never enter her yard. Her kids would never enter mine!
It's a matter of raising your children to respect others and to respect nature and animals. Mine were raised with many pets that they were taught from infancy to love and care for. My son's (I have 3) love to throw rocks into the water at the beach...if nobody's in the water. My daughter, (the oldest) is the enforcer when I'm not around. We also count on our animal friends to give lessons in behavior...
There's one child, well, she's not really a child anymore at almost 17, who has behavioral issues...
I have a honey bee hive in the back of my property...yep, she figured she'd check out the residents without asking, several years ago...I didn't have to say a word...buzzy and company gave her a lesson in etiquette.
She hasn't been back.