Depends on if mom took off and did not return - leaving these two very young girls in a dangerous situation. I cannot support that. However, if the mom drove off just out of sight, waited a short time, and then returned and ask if they were ready to behave - that I can see.
It may turn out that the Mom drove around the corner thinking the girls would come to her - however, once the older one “caught up to her” the younger one wasn’t with her and the Mom still drove home THEN called the police?