You can install any door look up high and be safe. But if your door knobs are round then just get the children proof door knob covers. The slip or pop on your knobs and require being squeeze to grip to open. Should be fine for a few years. Now if an adult has weak grip they may have issue with opening the door. Hardware stores should have them,even Walmart.
Man forgot to say, ENJOY THEM. It will not be long and you will miss those little steps. What a blessing grands are.
I did see the outer knob one, was wondering how much squeeze it would take to open, grip not what it use to be.