Unknowingly backed into car

So I thought I may have backed into a car while picking my son up from school. I really didn’t think I got the car, I honestly thought I backed into a chunk of ice and snow. I had my baby in the car at the time who was screaming so I didn’t really hear nothing. Well I get home and check out my car and there is a small scratch and another spot where a bit of paint is missing. Now I know I should of stopped when I was there if I was really wondering but I was tired, sick and had crabby kids and honesty didn’t think I actually hit anything. What should I do now? File a police report? I’m scared to death now.