These days, with all the kidnappings and lack of trust among people, its safe to practice the following when you find a missing child.
When you find the child, find the closest establishment and call the police from that place, and wait for the police to come.
Do not attempt to take the child to the police station by yourself. Even if you find the child in a crowded shopping mall, go to the nearest shop and ask them to call the mall security to the shop premise. It is safer this way than for someone to see you holding the child's hand and walking in the mall. In current times, no amount of explanation seems to satisfy others that you mean well.
So, for your own safety, it pays to be safe when helping others. There is no point in jeopardizing our own safety and well being when all we have is good intentions.
And the child, being young, cannot defend your actions. Children will believe whatever their parents say.