It's a 'crate', not a 'cage', honestly! There is some very good advice on the internet about crate training. I used a crate with an 8 month old foster dog, who had a very difficult start in life. She then spent 8 weeks in her first proper home, but was crated for long periods, without any training/preparation for that. She destroyed two crates, when frantically trying to escape from them. She had classic signs of separation anxiety, i.e. howled, showed destructive behaviour when left. I was told she'd howl and bark all night. She cried on the first night, whimpered really, for about 10 minutes, then slept all night. The following night she whimpered for 5 minutes, and after that, never cried at all. I'd say 'bed time', my 2 dogs would go into their beds, and the foster dog into her bed, which was inside her crate. She was fed in the crate, and definitely began to see it as her safe place. She always slept in her crate if she went for a nap during the day. Crate training has its place, and can be very helpful for anxious dogs in particular.
A number of comments are saying the OP's dog should either be re-homed where there are no children or put to sleep. My vet has been brilliant with my own dogs, and foster dogs. His firm view is that cases of aggression in dogs are very rare. The kind of behaviour shown by the OP's dog, and by a couple of dogs I've cared for, is usually caused by fear/anxiety of some kind. It is usually workable with, as long as the handler is prepared to work closely with a behaviourist, as Seasider clearly is.