I wouldn’t say it was “immoral” to not tell a child they were adopted, but they have every right to know. Mind you, it could be a lie by ommission.
I was adopted and I’ve always known.
I also have a few friends who were also adopted and the ones that find out by accident didn’t deal with it very well, of course, that’s not to say all children who find out by accident won’t deal with it,
But its part of who you are, there’s always that “who am I? where did I come from?” question that is important for every person to develop and understand. And kids aren’t stupid, they can guess if something isn’t right, or if they over hear something from relatives that gets them wondering, and usually when that happens they can pull away from their family thinking they dont’ really belong.
Yes, there can be circumstances where teh adoption took place under less than pleasant terms, but the child should still be told they were adopted and then if they so desire they can follow up with any investigation. A friend of mine found out she was not only a rape baby, but that the rapist was her biological mother’s uncle! However, she was glad she knew this beause she said she was now prepared if her biological mother ever tried to contact her.
If anything, its important to know for medical reasons. As I mentioned, I always knew, but I had no desire to seek my biological family because I was happy where I was, but my biological mother sought me and essentially forced herself into my life. (Which is another eason why the child should knwo, better hearing it from the parents who raised them then from a complete stranger contacting them saying “I’m yoru mum”). But when I met my biological mother I found out a raft of medical problems that affect any future children I may have. I also found out about an eye problem that would not have been picked up had I not had a name to suggest to the opthamologist.