Fired my babysitter

Well I'm in a situation here! Fired my babysitter due to putting my child in harms way. I no longer have a sitter and don't know what to do about work.

My sitter has had my niece in her care for 6 years. I've known the sitter for 10 years. Little back story, we went to school together and her and her husband are friends of my ex. They agreed that it wouldn't be a problem since they don't speak to the ex and he is out of state. Plus this is business.

Now as of yesterday I've had two situations with my sitter who has done things I don't care for with my son. Which we talked about and moved on. Well on July 24th she asked to take my son who is 10 months old swimming. My husband and I both agreed we weren't comfortable with they and said no. She agreed and they didn't go. Now July 25th comes and I take him to the sitter and pick him up. My sitters husband comes into the living room as I'm playing with my son packing his stuff and says "you won't like this but I took your son on the four wheeler"

I was livid. Just packed up and left. Well i immediately started asking around for a sitter on FB. Which of course she found out about. So I told her she put my son in harms way, and tried to hide it. My son comes first and that was not ok. She claims it's not a big deal. No one would intentionally hurt him. But who takes someone else's child on an ATV at 10 months old without permission.??!? That is crazy in my opinion.

Was I in the wrong here? Should I not have over reacted to the situation?

Now I need to find and start interviewing people for a replacement.