juxtapose

So my new dog..well, he bit my son. I don't think he is used to kids. He always gets annoyed with him, now I'm worried. Today wasn't the first time he bit him.
He bit him once before cuz my son was being too hyper and loud and I think he startled him in a bad way....BITE!
Then once when they were in the back of the car for a ride. Not sure why? BITE!
Then today he really bit him. He was home alone with him. My son says he accidently tripped over him..then BITE! Today he broke through his skin, he has a cut and a big circle cut..he was bleeding.
I don't know what to do.........
This is out first doggie...a hand me down older doggie.
Maybe he should be with another family without kids?
Any advice?