My child runs off if I let go of their hand. How can I teach safety?

Keep safety the top priority first. Holding hands, using a harness or wrist strap, or using a stroller are realistic safeguards for dangerous moments and are perfectly fine. Alongside that, practice a "stop" signal (the word plus a palm-out hand sign) as a game in safe places, and praise it right away when they do it. In parking lots and on roads, decide concretely on a place where you hold hands with an adult, and confirm the agreement before setting out. If running off is sudden, frequent, and hard to control, or you worry about wandering, also consider carrying a GPS or ID and sharing with the preschool/school.