@Maureen488 Cool listing, I'm a big fan of interesting color contrasts.
Unfortunately there isn't a setting that distinguishes a child from an adult in the maximum guest count. So as long as your max is set to 4 guests, you will find yourself declining a lot of requests.
Looking at your flat's layout, though, if you don't mind the suggestion I think a family of 4 might not be your ideal target group. The dining table, for example, looks like it can only comfortably seat 3 people, and two children who are young enough to be comfortable sharing a sofa-bed with their siblings would feel rather hemmed-in by the lack of space to run around in. Not to mention the headache at cleaning time.
My suggestion would be to cap your guest count at 3, which in Airbnb terms could mean 3 adults, 1 adult and two kids, or 2 adults and 1 kid (don't forget, if you advertise as "suitable for children" Airbnb automatically excludes children under 2 from the guest count, so that's a whole other story).