We can argue when life begins until the cows come home. We're not going to agree. Based on current medical knowledge, my opinion is that there is no self-awareness in an early stage fetus. Based on my lack of belief in a soul, a fetus has no potential for personhood until someone else projects that potential onto it.
Thus, my stated position, opinion or not, is that a fetus is much, much different than a four-year-old child. So, no, euthanizing a four-year-old is not my position.
I was a Christian when I had an abortion. Life experience and a deconversion to atheism has strengthened my commitment to the pro-choice position, but I have been pro-choice since I understood what abortion was. So, religion isn't really the basis for my position, either.
I'll stop now. I stated my opinion in raw, angry terms -- which I should not have done to begin with -- and it's led you and I to persuading each other of little but how deeply we can cut with words. My apologies for deviating from my ideal of civilized discourse; I'll see you around the forum.