I am a young Mom, and I have three children. None of them have the same father (please don't judge, I'm aware how bad this sounds) My oldest daughter doesn't know that her and her sister don't share the same dad. She is 5. My middle daughter is 3 and my youngest is 2. I married the father of my youngest child. We recently saw a doctor and he was asking about the 'family tree' and I had to explain that my oldest daughter has a different father but she doesn't know, and he said that the younger they are, the better it is to tell them, but I'm conflicted. I'm not sure if 5 is old enough to understand the situation, or if this will cause problems in her social life, or her self esteem... she's a very VERY emotional, sensitive little girl, and her bio dad isn't someone that I would openly agree to being part of her life, but I feel if I wait until she's older that she may resent me for not telling her sooner which could cause problems in her teen years. How/when do I tell her and how do I avoid conflict and self-esteem issues for her?

I subscribe to the general child-rearing notion that you do what makes you feel most comfortable and that which intuitively feels best for you and your child, most of the time. And this would be one of those times. I don't know where your doctor gets his theories from. It seems to me that a 5 year old will just get all confused about your husband. I'd wait as long as you want! I don't think it's when you say it, but how you say it.

Why has she always not had a photo of her dad and told that is her daddy ?

If not 5 when, do they have different last names ?