@Sami459 Don't open yourself up for trouble. Keep the boxes checked, in the drop down where you explain why the unit isn't suitable outline the safety issues that exist. I would not put that children are not allowed anywhere else.
You will have to be diligent in your communications with guests in terms of ensuring they have the correct number of guests checked, etc. etc. You could require in your house rules that you have the name and age of each guest, but I doubt you will need to do that. If people with children request your place, tell them to withdraw the request because due to safety issues the property is not suitable for children. The end.
ETA if you have Instant Book on, put in your automatic greeting message that due to safety concerns children under 12 are not permitted at the property, and if a guest has made this reservation in error they can cancel with no penalty...something like that.