Should I try and get my staffy back?

Writing this through tears so bare with me.
Basically, we brought our blue staffy at 8 weeks. He is beautiful. We have 4 children that are quite boisterous and play fight etc. My youngest is 1 years old and has really bonded with him, as has my eldest who’s 12.
I hired a dog trainer/walker who has been amazing and patient with us. Took him for walks every day.
So the situation I’m in now is this...!
During the weeks school holidays my kids were in and out the house, playing with the neighbours etc! I put him in his crate as it was quite manic.
2 of the neighbours stood at his crate and my dog went crazy, barking growling etc! He’s never Shown at agression in the last year so it was really alarming!
The dog trainer came round and advised us that the house was too busy and our dog was feeling anxious. He advised no more strange kids in the house! I spoke to their mum and told her that I don’t want to risk anything happening to her kids and to stop them walking in, which she of course agreed to.
Yesterday the neighbours 5 year old daughter let herself in without knocking. I was just sitting on the sofa with him stroking him! He was very calm!
He heard her come in and jumped off the sofa, ran upto her and bit her on the face! Hard enough to draw blood and bruise her face. I instantly rang my dog trainer who came straight away and took him! He said he warned us this would happen!
He said that their is far too much human traffic and it’s not safe now that he has bitten a child!
He’s never done anything like this before, he’s been amazing with my children.
In a panic I gave him all of my dogs kc papers, his microchip details and that was that, he was gone.
We are all devastated and miss him terribly! It’s only been a day! He’s msged me today and said that he had found him a lovely home with a couple that have a huge garden and surrounded by fields! He will still be walking him every day and the house is very quiet with another dog that my dog plays with daily. I want to do the right thing and I trust my dog trainer completely! But he’s my dog and we love him so much. He had the best of everything with us! Days out, the most expensive food, lots of affection and attention! He was loved so much!
My children are in bits over it and keep crying. The little girl who was bitten is thankfully fine! It was more a warning nip then an actual bite but enough to draw blood and bruise her a little. Obviously I wouldn’t want to risk another child being hurt or for him to be put down.
Do I just let him go? Am I being selfish by wanting him back? Is it too late to even get him back now that he has the paperwork? Will my dog be missing us?
I’m in such a state over it and want what’s best for him but can’t help but think it wasn’t his or our fault.

Your trainer/dog walker has no legal right to remove your dog without your consent, neither does he have the legal right to rehome him.

Did you sign anything? 

The trainer is not a council warden or a police officer. 

Having said that, if you do get your dog back, what steps will you take to ensure this never happens again? Have the child's family reported the bite to the police?

Thankyou for replying.
I was in a panic and he said it’s best he take him! I agreed! Iv had a day to think it through and seen/felt how devastated we all are without him here.
He even said ‘Iv been lining someone up for a while because I knew this was going to happen’!
They haven’t reported the bite , they were very understanding and upset that she had just wandered into our house. To be honest, it’s more a nip then an actual bite. There’s a tiny mark on her face this morning. I know potentially it could be worse which is why I would put steps in place. I would keep the front door locked at all times for one.
He’s been barking a lot this week at every single noise so I know he’s been unsettled with all the chaos of the kids being off school. I would have to definitely be stricter on my children regarding noise and letting people in etc. They would adhere to it if they knew he was coming home.
He has all of his paperwork so I don’t know if I can just demand it all back. He’s still registered with me though so I’m assuming he’s still technically mine?

Kennel Club paperwork us not proof of ownership - your purchase receipt is! 

He has no right, no matter what state you were in, to keep your dog. Tell him (politely to start with) that you are prepared to work harder with him & you want him handed back NOW. 

Then contact a properly qualified behaviourist & book a one-to-one session. This 'trainer' is NOT qualified to do anything with your dog if this is the way he's behaving.

If he still refuses to hand him over, tell him you will contact the police and report a theft.

I’ve spoken to him at length. It is, unfortunately the right thing to do. As sad as I feel about it and as much as we will miss him. The fact is, he did draw blood which automatically makes him a threat to children in the eyes of authorities. We are lucky he wasn’t euthanised.
He’s sent photos of his new home and it’s beautiful! Huge garden and another dog that he already walks with most days. They are retired with no children so perfect for him.
I think it’s a combination of too many children in my house, too noisy and chaotic for him as well as no real pack leader. My partner works long hours, I’m home with 4 children and always occupied!
He was my first dog and I had no clue really what I was doing. My partner wanted him but changed jobs 3 months ago. So basically left to me.
Didn’t realise quite how attatched I had gotten to him. It’s like giving away a family member, very painful.
Thankfully he has been found a lovely home and will get the time and attention he deserves.
Lesson learnt. Just a shame for everyone involved really. The little girl that got bitten. My kids that are attatched already, the dog and myself!
Thankyou for the advice x

Okay. 

But please, 
a) Ignore the 'pack leader' thing - it's old hat & mostly discounted amongst modern trainers. 
b) Yes, your situation was difficult, but no more difficult than hundreds of other mums! He should NOT have taken your dog without first having several in depth discussions with you! Your dog is NOT vicious, neither us he out of control. As a trainer, he should have been able to work through ths with you. 

Personally, j feel you've been duped. He made his mind up from an early stage that you couldn't cope & therefore didn't want to/couldn't help you.

Put it all down to experience. But next time, if you have a problem, ask the people who KNOW Staffords for advice & direction. 

In no way am I blaming you for what has happened - I blame the 'trainer' for not advising you when he "knew it was going to happen". Not good enough!

I know you have come to terms with it all, but just to reassure you frankly if your dog has bitten a child in the face, i would not want to have that dog in the house with 4 young children. Training and whatever can only go so far. Staffys are very family friendly IN GENERAL but that does not mean every staffy will be. Each dog has their own personality and your dog may just have had the personality to like things a little calmer. No amount of training will take a personality trait away.

I agree that the trainer should have been a little more open with you and shared their concerns but i can also understand they are there to train the dog for you and probably assume that if they say you need to get rid of him you would have just said no and fired him.

Im sure the doggo will have a great life now and if you ever decide to get a dog again im sure you will do it in a more informative way.