You have my sympathy OP - I have been going through almost exactly the same thing.
Working Cocker spaniel, not quite two. Last year he bit my (adult) DD, not to blame her as he shouldn't have done it, but he had a chew, and we were already aware that he growls and guards chews and were working on training around that, but she bent down to kiss him and he bit her, catching her lip. She needed three stitches, (as well as antibiotics and tetanus obv) and the scars are barely visible now unless you are looking for them.
We rationalised he was only eight months, still a pup, lots of training to be done.
Soon after that we took him to the vet to be neutered, but the vet rang up and said he was guarding his cage and neutering could make his behaviour worse so she refused to do it.
Despite consistent training around guarding chews he has continued to do so. Only 3 or 4 weeks ago he had a chew, lying at my feet. I rubbed his tummy with my foot and he growled at me.
We had him neutered in the end about three months ago, as although he is never aggressive with other dogs, he wants to play, but doesn't back down when other dogs don't want to play and I was concerned he was developing dominant behaviours and could get in a fight which wouldn't really be his fault but might then lead to more aggressive behaviour. We have had him going out with a dog walker once a week so he gets a good walk with other dogs all on the lead, and I had thought that was improving his behaviour.
He did seem to be calming down a bit after neutering.
But two weeks ago he was asleep on the sofa with me sitting next to him. I bent over to cuddle him and he launched himself at my face biting my nose, I had cuts either side, one very close to my eye.
Headed off to A&E bleeding profusely. Heard someone say she'd been waiting ten hours as I walked in (late at night). Waited two hours to see triage nurse who confirmed they were superficial cuts and no stitches needed and I'd have to wait eight hours to be seen to get antibiotics and tetanus 🙄.
So I went home and went to my local minor injuries unit first thing in the morning where I had a short wait, efficient nurse and got the tetanus and antibiotics in a five minute consultation.
Had a long chat with the vet on my way home who offered to refer to a behaviourist but agreed rehoming was probably for the best.
Now I will say, I have never allowed dogs on the sofa before but this boy was such a cuddly puppy, I couldn't resist. And I recognise, for some dogs at least and he is one of those dogs, not allowing the dog on the sofa is not just about dirt, but much more about pack position, and he needed to know his place. Also that old saying "let sleeping dogs lie". Maybe I just startled him.
What ever, I cannot trust him again, and the next bite could be much worse. Although my adult DDs are nowhere near planning for babies, it has been at the back of my mind before this that if a grandchild came along, I'd have to send the dog to kennels or something every time they came to stay.
We all agreed he is a working dog, he came from a game keeper and working stock. We have found a home with a local gamekeeper. I feel so sad, thinking how he must be missing cuddles and toys and treats, he must be so confused, but I know he will respond better to having just one trainer, and the company of other dogs and lots of work. So far he seems pleased with him and says he is loving going out with the dogs, comes back well (he has good recall to the whistle, he's a good dog in many ways) and I know I made the right decision. He's an incredibly energetic dog, the only time he has been tired and settled in the evening has been on holiday in Cornwall with lots of swimming all day.
Two hours a day isn't enough for him, he needs to be on the go all the time and he's getting that now.
So I sympathise OP, but you know what you have to do. There will be a good home for him out there, he's only a young dog with lots of potential for a good life, but away from children.