This is a topic that is close to me, and consequently will be a bit hard to write.  I am a strong advocator for children having the right to know both parents, yet my own history is all mixed up in this regard.  From the outside it may appear

When I was in my mid 20's, my father passed away, after which my mother revealed to my brother and I the little family secret - we had an older half brother.  Apparently my father first became a father at the very young age of about 18, and obviously he and the mother didn't stay together - though I don't know any of the details.  If I had known this during my early teenage years, I know that I would have caused no end of trouble about it.  I would have been asking questions that I didn't really want the answers to, saying things I didn't mean, and trying to locate a relative that no one in the family could even confirm the name of.  Had I found my older half brother, I no doubt would have caused him and his family no end of grief as well.  (Yeah, I was a troubled teen to the nth degree). I certainly know I would have made things very difficult and emotionally turbulant for my father.  Neither my family nor my half brother's family deserved that.  However, because I wasn't told of this until much later, I accepted the news with an understanding that these things happen in people's lives, and without expectation that any member of my family would be immune to these things, and so it didn't cause me too much surprise.  I filed the infomation away in the back of my mind, and although I often wonder about what it would be like to meet this person, I have no desire to track him down.  If he came looking for his father, then I'd be happy to meet him.

My daughter doesn't know that I exist.  When she was born I was very unwell.  I couldn't even look after myself let alone a child.  So, for her sake, her father and I arranged for her to live with him until I could get on my feet again.  As soon as the court formally gave him full custody, he made seeing her difficult at best.  Because I was so unwell, and I had very little support from friends and family, I could not deal with having to drag his butt back to court every time he stuffed around with her right to see me.  The agreement would be that I'd see her on a certain day for a certain time, and when that time came, suddenly he couldn't bring her to see me until hours later, and had to pick her up hours earlier, if indeed I could see her at all.  In the end, for the sake of my health I had to just give up and step away and hope to catch up later.  By the time I was well enough to fight against his attempts to deter her from knowing me, quite a number of years had passed.

Her father had married and raised my daughter with the belief that his wife was her mother and she had no idea I even existed.  This was totally wrong in my opinion and it infuriated me.  However, I had to put her first.  For me to step in via the courts and demand that she be given her right to know me would have been extremely disruptive to her.  She was at the age where it would be so very easy for her father to try and turn her against me with nasty stories and BS, and she was reaching the age where she had a voice and could decide she didn't want to see me.  If he filled her head with enough rubbish, it was quite likely that she wouldn't want to know me.  I did not want to see my daughter torn between two parents, having her mind filled with doubt and confusion, and having to live in a realm of hostility that she so far hadn't experienced.  I felt that it was better to leave her in blissful ignorance and not know me for the time being.  When she is older and mature enough to accept that I am her biological mother, her step-mother loves her and is also her mum and she must respect that, and she can make up her own mind about what sort of person I am without being influenced by other people's opinions, then I will make an effort to allow her to know me.  Until then, I will wait patiently for a phone call.  I now live in a different city, but I have good friends that regularly give me reports on how she is doing, so if she learns of my existance earlier than I expect, I trust someone will let me know.

My oldest son's father I don't know myself.  It was a nasty way that my boy was conceived, and at the time I couldn't handle the whole thing of going through court, so I didn't even bother to report it - yeah I know, I should have.  A few weeks later I found out that I was pregnant.  I ended up getting married not long after my boy was born, and he has grown up knowing my ex-hubby as his dad.  He now has also chosen to call my boyfriend dad as well.  I have explained to him that he has a biological father and that he can't see him because we don't know who he is.  He is quite content to live with that knowledge.  If he chose to try to find his father later on in life I would support him in that.  I am not keen to do it myself as I don't know how I would be able to handle dealing with it all.  If anyone else was in the same circumstance I wouldn't blame them for making the same choice, so I will not feel guilty about my decision.  My son is also aware that he has an older sister that he can't see yet because she lives in another city and doesn't know about us.

Right from the start, from the time they are born, children should know the basic truth.  If they can grow up knowing both of their parents, then it should be so.  If for some reason they can't know a parent, they should at least know of their existance so that it doesn't come as a shock to them later on.  However, depending on the circumstances, if the child was not raised with this knowledge from a young age, it may sometimes be better if the secret remains for just a few years longer, until the child is old enough to deal with the knowledge without it causing a major disruption to their life.  If someone can explain it to them in the right way, and the child has the right sort of support, then by all means it should be explained as soon as possible, regardless of age.  I'm talking about situations where the only way the child will find out is by forcing the issue and going to court.  This can rock the boat a bit too much and be quite detrimental to the child if the parent they live with is being very stubborn about keeping the child from knowing their other parent.  Once the child is mature enough, they can get to know their other parent on their own terms, make their own judgements about the adult that was missing from their life, and can better see and understand both sides of the story as to why they couldn't see them and know about them in growing up.

I would recommend that if you are holding such a secret from your child, that you explain it to them.  Make a quiet time to do it today.  They will eventually discover that they have a parent they don't know, and they may become quite resentful towards you for not telling them - especially if you had no good reason other than you don't like the person.  If the reasons for not being able to see their other parent are legitimate, that is a different matter.  By all means, we still have to protect our children from being hurt, but that doesn't take away their right to know the basic truth.  I recommend that you still tell them of the existance of the other parent - even if you have to be ambiguous about why they can't see them.  And don't make the mistake of telling lies about or speaking ill of the other parent.  After all, your children will find out the truth one day - and how will that make you look?