Some models of refrigeration appliances offer you the feature of a child lock, or they can be
purchased seperatley from most manufacturers. In most cases they can be got in a suitable colour
to the fridge or they can be clear plastic which also means that the refrigerator lock is less noticeable.
While it's not invisible, the the fact that it's 'camouflaged' means it attracts less attention.
The idea of the refrigerator lock requires that you PUSH the door in to disengage the lock.
So unless they see how you operate it, they may not work it out.