children don't have much prejudice before they learn it from others. they learn from adults that there are some opinions that you're supposed to have, and from their peers what opinions you have to have in order to not be excluded from their group. but parents will be their primary source of morals and ethics.
the child may be ashamed to talk about their dad having been a woman, but probably not until they're around 7-8 years old. that's when they start to forcefully try to get rid of their childishness in order to fit in with older kids, pretending to be more mature than they are. before that, they are rather honest about what they think is fun or lame or just weird.
if you tell your child, i think it would be better to tell it early. maybe even have some pics in an album of your time as a woman. so they get used to it and are able to think it's a natural thing. they won't learn otherwise until kids or adults in kindergarten or school start pointing out how that's not normal at all. so if you tell, prepare to also be very open about it with the teachers. and with your kid's friends. and remember that kids don't need that whole transgender explanation, even in their first years in school, it will be enough to just say that it's so much cooler to be a man, and that you became one because you wanted to. kids are very open to an honest opinion being the truth rather than symptoms of some mental disorder. only adults are that narrow minded.
do remember that the child is likely to find out that you used to be a woman even if you don't tell them. learning that everything was a lie is more likely to scar a child, than having known their whole life. i know a story about someone who was adopted and raised by the most loving parents ever. he was never treated differently, and there was genuine love and trust between them. all until the day in the child's early adulthood when he learned that he was adopted. the bond broke, and nothing the parents did could fix it, because the feeling of having been deceived by one's own parents (or who one thought were one's own parents), was that damaging. he left them, and never came back.
honesty, and treating the matter like something natural, while also preparing the child for some of society's reactions, might be safer than betting on the child never find out or reacting negatively to your hidden past.
