@Richard2445 As you’ve discovered, there is no setting that distinguishes a child from an adult. As long as your max is set to 4 guests, you will find yourself declining a lot of requests. Adding text about your ideal group to your description will not help.
A few thoughts. A family might not be your ideal target group. The space is small and not looking super child friendly. A sofa bed is not a bed and should not be listed as such. Any adult that ends up sleeping on it may earn you lower ratings if it results in less than a great night sleep. The fact the bathroom is an en-suite could be problematic for a group of 3 adults, or even two friends traveling together. I think your ideal target is couples.
“….we had a request for 4 adults, so we decided not to send a confirmation response. Then we noticed AirBnB blocked the dates they were requesting, my guess is because we did not confirm??????”
A Trip Request requires you to either decline or accept. If you ignore it, it expires after 24 hours and the dates are blocked. You can manually unblock them though. The following article explains in great depth everything you need to know about Requests and Inquiries.
https://www.airbnb.ca/resources/hosting-homes/a/understanding-response-rate-and-acceptance-rate-86