I realize this is nearly 2 weeks old now that I am reading it but I just want you to know I am praying.
I am not sure I have ever met one mom that didn't have those "I must be the worst mother in the world" moments. I think if I was ever to meet one, she would probably be one who cared nothing for her kids. We all have those days, weeks, months, however long they last. Take some comfort in that.
When my oldest son was 2, he had found his dad's razor in the garbage and tried to shave with it - where was I? Why wasn't I keeping a better eye on him. Why didn't his dad put the razor in a different garbage? Well -because we are human and prone to make mistakes. Luckily, he only took off a little skin from the tip of his finger and had a little razor burn on his face - but it could have been so much worse.
The best we can do is trust our children to God and have Him lead and guide us through each step.