My children have a half sibling that they don’t know about or have contact with. My ex is not involved either and as far as I’m aware he doesn’t see the other child, my children don’t know about the other child and as time has gone on I guess it just got easier not bringing up the subject as they are unlikely to ever have any contact. But I’m wondering if this is the right thing or I should tell them? It just seems a bit off to say “you have a half sibling but you can’t see them though” any advice?