@Janice72
if your house rules states that you don't accomodate children then your guests shouldn't be able to instant book your place. But sometimes they book for adults only and mention kids just in message. That is not right and you can cancel their booking on that ground. But, don't cancel by yourself or you will be punished, you should contact Airbnb and ask them to cancel or tell your guest to cancel on his behalf.
However, I would advice you to turn off instant booking until you become familiar with how Airbnb works bc I see that you don't understand the basics jet and it could brings you into trouble.
Read this forum (as much as you can) ,FAQ, terms and conditions....