Saw this in the notes and figured I'd step in!
So, for non-SDV players, in most farming sims you can get married to certain characters and have children with them, however this is typically a permanent choice that can't be undone, so if you want to marry someone else or not have kids you would have to start over with a fresh save.
But SDV is different. The game has a witch's hut you can eventually unlock that lets you use...black magic, basically, to soft-reset marriage/children choices without starting over. There's a divorce option so you can ditch your spouse, but that's the only normal one. It also adds an option to turn your children into doves to get rid of them, hence OP saying they "birded" their kids. You're not...technically killing them...but only barely.
(It also adds an option to mind-wipe your previous spouse so they don't remember being married to you and thus don't hate you, and you can even remarry them then if you want, but I don't think that was needed for this, just figured it was sinister enough to warrant a mention.)
All that to say, the reddit OP married a character, progressed to the point that they had a child with them, and then used black magic to "kill" the child and divorce their spouse before moving on to the next marriage candidate and doing the same, over and over until they had gone through all twelve marriage candidates, resulting in a collection of twelve "dead" children.
Which, I must agree, is some uniquely unhinged behavior indeed.
