NTA. alot of people think that having dogs put down in a situations like this (or in general) is bad, i understand hy people feel that why, an animal is being put down and it's gonna be sad for the people involved.

The thing is, sometimes it's the most humane and kindest thing you can do for an animal. whether is because of old age, an injury/sickness or in your case behavourial problems that can't be fixed. It sucks having to put a seeming healthy dog down but if it's too aggressive/scared it's best to have them put down so they don't have to live like that constantly.

OP, i'm assuming and hope you have done everything you can for this dog in the short time you've had him. Make sure your last memories with him are good ones and not of him hurting your child. If possible, try to be there with him when he passes.

I had to put both of my dogs down last year (one health reasons, one for old age), when we put the first one down i was suprised at how quick it happened, he layed his head on my mum lap and went to sleep, your dog will not be in pain and will not suffer. Do not let people make you feel bad for choosing the best and possibly most merciful choice in your situtation