Hi, I have two children and I am very familiar with your situation. Once the kids went to the store together, which is a mile away from the house, and disappeared for several hours. My husband and I called them probably 30 times, went to that store and they weren't there, and when I wanted to call the police they came. It turned out they had met some friends and were playing with them. After this incident, my sister advised me site
https://bestparentalcontrolapps.com/how-to-track-an-iphone/ after viewing it I realized that I can track their geolocation at any time. This is very convenient because if the kids don't pick up the phone again I will always know where they are.