Once my grandson was crawling pretty well, he discovered the kitchen cabinets and it was time to do something to keep him from getting hurt. When our children were little, we bought a set of latches that were pretty effective, so we tried it again this time.
About the same time, I recalled why we had taken the latches off the doors when my son was still small; he had been nearby when one of the cabinets was opened and he received an ugly scratch across his arm. It could just as easily been his eye.
It is simple and cheap and so far, my grandson hasn't figured it out.
The heart of this project is merely to loop a piece of 550 cord around the cabinet door knobs and anchor it to the inside.
The materials needed are about 8-10 inches of 550 cord and a small screw eye per door (or pair of doors, depending how your knobs are situated.) You also need a cigarette lighter to melt each end of the cord and a drill with the appropriate sized bit to drill pilot holes for the screw eyes,
First, drill a small hole where you want your screw eye. This should be on the door stile,on the opposite side from the knob. (On the back of the door frame, in other words.) Screw it in.