She knows about the baby growing in a mommy's belly, how he swims around in "water" until he gets too big, and how he finally comes out. She also knows what an aborted baby looks like, and that it it is a killed baby, and that doing so is evil epitomized. She needs to know the truth about the people around her - who they really are as evidenced by what they continually vote to keep "safe and legal" - and know she will. She is a perfectly normal, happy, giggly four-year-old.
My other children will likewise learn about these things when they are a little older (aged 3 or 4).
Not saying everyone should do this, just saying that is how it is for my children. I will not lie to them about the most common cause of death of children, or about the people around them who think it's just dandy.
I respect your experience. My kids, too, knew about healthy frisky fetuses (!) and loved them from a very young age. But I personally wouldn't want them, when they were little ones, to have known that many of the mommies they saw around them have murdered babies. It would be frightening, I think, and give them a vision of depravity which I do not think it is reasonable for little children to bear.
It's a question of age and sensitivity. It's like knowing about rape or torture. They may know "what it is," but they don't have to have vivid images of it seared into their minds.