Whew! Deep breath! Kids will be kids, and at age 4 they have a hard time controlling their emotions. Yes, it was shocking your son hurt your pup on purpose but maybe your reaction was a little extreme. Everyone has their bad mommy moments.

I would agree with Karlin, put your pup in a crate while traveling in the car. It will be safer for everyone.

Just FYI, I have small kids too and I have had the same incident happen with my pup and child. You know what, the pup forgot about it quickly and the child moved on. I would never let my child abuse an animal but I would base my punishment on the age of the child. Hug your kid and tell him you were sorry for yelling but remind him in your home people are nice to animals. You also should have an action plan in place if this occurs again.