Okay, F. B., here's the thing. Don't lock your toilet....if your little one can get in the bathroom at all they can turn on the water in the sink if they can climb up that high. They can climb over into the tub and get that water going and drown just as easy and they can tip over into the toilet and drown.
Babies aren't at risk as much as toddlers for this death though. So it's older ones that are in need of protection.
Go to Walmart or a hardware store like Home Depot and buy door knob protectors. Kids will figure them out soon enough but for now your little one can't reach them and hang on them enough to make the rubber part inside stick THEN turn the door knob protector while holding it down...they just don't have the needed strength and skills. By the time they're potty training and stuff you can take them off.
The part that is on the side...it has rubber on it so when you pinch or push on that area then turn the knob it turned the knob inside. Little ones can't do all that.
https://www.google.com/shopping/product/17692898429783202...