This is becoming an issue in our house. We have teenage kids. Our eldest has a key for our house and one for his Dads since year 7, never any problems or keys lost.
DSS and DD now want a key as they have started high school, the problem there is that DSS's DM is a nightmare and we know that if she got her hands on a key to our house she would use it. So the result is that neither of them have a key, but sometimes they do need one. I give DD one and she returns it when I get home. This only happens once a month or so as there is someone at home each day when they get home from school.
Anyone else had this issue? How do you manage to give the kids freedom with maintaining security at home?