A comment like that would be an unprofessional and completely inappropriate lapse. Unless she confessed to your husband that those were her actual words, though, I hope you will keep the possibility open that even though that is what your son heard/interpreted, she may have actually said "I hate when kids…." Even that is a lapse in judgement, and shocking enough that your son may have "heard" that she hated HIM.
I'm so sad for your son to hear of his experience, either way. I have had a few events in my life where people I liked and respected suddenly blurted out some harsh judgement, against me or someone else I cared about. I was certain in each case that they said something worse than they did, as corroborated later by witnesses to the comments. When one is shocked by an unexpected occurrence, the take-away memory can be much bigger than the actual event or comment. Nevertheless, that take-away can be devastating.
My suggestion would be that you give yourself enough time to cool off, and talk to the teacher yourself before taking this further. It's a courtesy that you would hope to receive yourself if you were at the center of a controversy.
If I were you, I'd want to hear her side of the story, because there could be something there that bring new understanding, or can soften your feelings toward her. Then I would want to tell my son's version and the emotional aftermath he suffered (and may still be experiencing), and express my own anger. I'd tell her the effect her harsh words had on my whole family, and ask her if a child missing one day of school is a higher priority than a happy family reunion.
There is great relief in being able to say, "I hope you can see why it's been hard for me to even speak to you over the past ___(time)___. I was afraid I would just lose it, and I want you to know I am still furious. I am interested to know what you will do do make amends with my son, or whether I will need to take this issue to the principal."
She may rise to the occasion. She may sincerely apologize to you and your son. She may admit she was wrong, and has learned from the whole debacle. That wouldn't make the event go away, but it could put the rest of your son's school year on a positive footing.