Probably the simplest solution if the assumption holds that the ones trying to be kept out are too short to reach. Although don’t make the wife mad or you could get locked in from the outside…

Alternatively, assuming the door is only prepped with a door handle currently and you don’t want to drill more holes into the door, just Google a cheap push button style lock that fits the existing hole. Looks like there’s plenty of low security options around $20.

I’m certainly no expert but the guy’s eye movement looks pretty strange.