K.L.
First of all, this is a mother's worst nightmare, and I am terribly sorry that you have to deal with this. It is horrible.
You need to take your children to the doctor. Now. They will need to do an exam on them to make sure they are OK. They will help you report this to the police. I know this is going to be hard, but you can do it. You need to be strong and make your kids feel like it's OK and that you will protect them. Don't lose your cool in front of them. They need to feel safe with you right now.
Take them to the doctor immediately and call the police. Stay strong. You are their Mama, their protector, and you can do this.