The front door in my present home had one of those lever type door knobs. Nothing to turn, just pull it down and the door is unlocked and open.
As I learned, my then two year old could easily do that. One morning we could not find her anywhere in the house. In a panic I went outside to see her standing by some flowers out front. She had pulled on the handle, the door opened and out she went to explore the world.
I soon replaced the handle with one that required a good firm twist from a bigger and stronger hand. And I put a little flip-latch gizmo up high on the door frame that would keep the door from opening even if unlocked.
Our house also has those lever handles on the front door and garage door. We added little flip locks at the top of the door after a toddler escaped one afternoon. (Middle of the day, didn't make it past the porch.)