@Marie5884 Have it as a part of your property description. For example: "We are licensed and can host up to 4 humans --our cottage is ideal for two couples, or family units with no more than 2 children". I would also make sure that the guest knows that children "count" as AirBnB has some ridiculous language about children being free.
I did look at your listings -- with all of the bunk beds that you have, people are going to bring their 5 or 6 chidren. If you don't want more than 2 children at a time, change your beds to "marital" types and reduce your numbers.