First of all, @Lesley143, your home is so charming! What a great experience for a family traveling in that area of France. Theft is extremely difficult to prove and thus difficult to claim. However, if you have a way to prove the theft by one guest prior to another guest arriving, you should be sure to have sufficient security deposit to cover expected loss.
You are letting strangers into your lovely home in another country, so if you think this may be a frequent occurance, you need to find a way to manage the guest check out process that takes stock of all items. Can the cleaning person do that for you? Have a check list of items and have the cleaner check off the items, preferably while the guest is in process of leaving.
Another direction would be to stock the kitchen with items that have little monetary expenditure and incorporate theft into your rate. You can find many of the items at thrift store or second hand stores without losing the charm of your place.