I'm thinking of showing the child my private parts inside my pants.
Why do you want to show your private parts to a child?
I don't get why that is unacceptable?
Children shouldn't be seeing the private parts of adults. If you expose yourself to a child you could get arrested and sentenced to prison. People will also think you are a pedophile. When children are old enough, they will learn about anatomy in a classroom setting.
I doubt she would feel embarrassed about a normal human body part.
You don't know how a child will react if you expose yourself, but we both know that the consequences for doing so could be severe. So even if you don't think it is wrong to do so, I have to urge you to at least just avoid the trouble that will inevitably follow.