Depends on which lore you follow, He was groomed from very young, and I hate this, but new canon has made Sidious the one that impregnated Anis mom, with the force that is.
...Plagueis and Palpatine creating Anakin is a part of Legends continuity, not new Disney canon, as part of the Darth Plagueis novel, released in 2012. Though Acolyte does imply they're going to also establish that in Disney canon as well.
Wasn't it the opposite? Plagueis tried to corrupt the living force and create life but the force was so disgusted by him that it cut him out and created Anakin as the counter the tilt?
Plagueis wanted to create perfect force life but was cut off. The living force was Anakin's other procreator.
Could be completely wrong. I saw all of this in a Sheev Talks video where I was so sure he was referencing a canon book.
(The earliest I'll give you is when he killed the younglings, I actually want Disney to do a Lucas remaster and have his saber turn red during that scene and straight up gaslight the world saying it was always like that).
LOL, that would be kind of hilarious. It would mess with the timeline ("your father wanted you to have this") and the preexisting lore of "tortured kybercrystals" though.