I completely empathise. 
We got a working terrier at 8 weeks. She showed "bad temper" in the first week (snarling and snapping and thrashing around when handled) which we took in our stride as "testing boundaries" and worked on training. The first time she set eyes on another dog that wasn't her breed (at 12 weeks) she SCREECHED like she was being murdered and had a fear of other dogs from that day forward. At puppy classes she hid under the chair and screamed in fear, after 3 classes I didn't take her back because she wasn't getting better.
We had that dog for 12 years, and it was hell on earth. She was okay when working and if given top spot with other dogs on the estate - all six dogs stayed out of her way - but she retired at 7 due to a spinal condition and could not greet or pass other dogs out in public as she would attack them (as in, she would actually go for their throat).
She was fine with us (I only got bitten twice, DH never, no DC) but with a few exceptions other people could not look at her or touch her as she'd lose the plot and go for them. She saw 6 behaviourists. She was on pain management medication for her spine. She had to be muzzled for the vet or for visitors where she couldn't be locked away. We had locks and warning notices on our gate. She bit someone badly on the doorstep and we were lucky not to be sued. She attacked my DH's 3 year old nephew (she was muzzled).
So many times we considered giving up and having her euthanised - our vet, who was a saint, said as owners we'd gone above and beyond with her. She was definitely a special needs dog - essentially I believe she just had a terrible temperament and her parents should never have been bred from.
I adored the little shite (we had a bond, she was frightened of life really and relied on me) and I cried buckets when we let her go last year because we couldn't manage her spinal pain any more - but to be honest, it was also a relief.
We've since got a new terrier puppy (a pure bred KC registered Border Terrier, not a working mix from a hunt kennels as she was), and we have been terrified of making minor mistakes with him and ending up with another reactive, aggressive dog. But he is the sweetest, most even tempered, amenable, passive and silly dog you can imagine. He is totally different and he'll be a year old soon. We haven't done anything differently really, but between the two dogs, his breeding and experiences between birth and 10 weeks are worlds apart.
But sometimes, I believe it really is just temperament. Best wishes to you - do what you need to do for your family and DC.