Every single part of this story screams bullshit and I don't believe it. At all. Every single comment he makes is contradictory towards the last, and is just a weaving story that makes zero sense.
He's dating a chick and she is abusive towards him. They have a kid together, she doesn't put his name on the Birth Certificate. This causes a rift so he dumps her, however he finds out she's pregnant again so gets back together with her. She does the exact same thing while he's working. So clearly he wasn't worried enough about what happened to make sure it didn't happen again. He can say "Oh she said she'd change and I trusted her" but that would immediately just be pointed out as bullshit as she's fucking abusive. He would have to sneak out of the window to get out of the house, so he knows well off that she's going to fucking lie. He failed his responsibility there to actually follow up on anything. So after he leaves the babymamma, he gets together with his girlfriend. They take care of the kids together and when baby-mamma realizes that she won't break them up, she bolts.
He, presumably, starts looking for her to get the kids back but can't find her. He calls police and everyone else, all of which say he has no rights as he's not on the birth certificate and wasn't married to her. Sometime later he gets a phone call saying he has to prove that he's the father with a DNA test. This goes through, SHE takes it as well, and it says he's the father. This forces him to pay child support to her, but not to see his kids. He has to pay her money, but doesn't know the address within which she lives. He can't find her specific address, but he knows what town she lives in. On top of that, to serve her papers he has to know where she is, but I guess is too lazy to go looking for himself. I mean he knows her, but doesn't possibly know where she might frequent or what kind of job she might have. He also claims to not be able to pay for a Private Investigator due to paying child support to his baby-mamma, and paying for his wife and himself. Yet he also claims to have a ton of support, but no one willing to chip in a couple pounds to try and save up for a PI. He says that she blocked him on social media, but a friend has a fake account with her on it waiting for her to 'slip up'. I guess she has zero identifying information at all on Facebook that points towards where she might be, including friends who aren't living in the same town or anything.
I don't believe it. It sounds like a really awfully written sob story just done up for attention. Very little of it is coherent or makes sense, and so much shit contradicts what he's saying. I've been reading /u/MrBagnall's history too, watching all of his updates to these comments and it just keeps piling up more and more shit that doesn't make sense. He should have just made the comment and moved on.