my sister is missing!

One day, me(Charlotte), my sister(Sophia), mom and dad went to a shop for some vegetables mom told me to take care of Sophia, then i wanted to go to the bathroom then i told a cashier to help me take care of her. the cashier said ok, so i went to the bathroom when i came back the cashier said "I just saw a lady fell on the floor so i helped her after, your sister disappeared! i am so sorry" then i said "thank you for telling me" then i went to tell mom and dad but they both disappeared then i went back home and saying to myself it's ok they will come back stay calm.....

part one