As long as you’re comfortable knowing that there are people who are still walking around with your house keys, then you don’t need to. A previous occupant could at any time just wander up to your front door and let themselves in. Of course, most people are not going to do this, but how confident are you that it has never happened to anybody?
This all comes down to peace of mind. It’s unlikely that somebody with a set of keys will just let themselves in, but you’re probably paying to insure yourself against lots of things that are just as unlikely to happen. It’s something to think about.
Our recommendation is to have your locks changed. You only need to do it once for peace of mind knowing your family is safe from the outside world and only trusted people have access to your home.