You're not the ones in the wrong OP, but you are the ones with the responsibility. Take a deep breath, you are upset, and we understand that.
If the dog was calmer and you weren't afraid for your children, would you want to keep him? He will take a lot of work and attention to get there.
If you can possibly afford it, pay for a session with a pet behaviourist. The vet reception, or a rescue centre may recommend one. The behaviourist will work out why the dog is so hard to handle, whether you are doing something wrong, have the wrong expectations, or whether you have a super challenging personality on your hands (they are often the most fun, once you sort them out!).
Put all the dogs food in the kong, so he has to work for it. He will end up with several meals a day, and lots of stimulation. Feed it to him while you are busy with other things and need some time.
Keep up the walks.
Watch dog training videos online. Victoria Stillwell does good ones, also look up Naughtybutnice training. There are little games you can play with him which only take a few minutes, but really build the bond which is what you need. NO Caesar Milan, please!
You need to be calm around him. He's got all over excited, and is playing rough. Calm him down by being calm yourself. No shouting, no squealing.
Good luck!