If you see a child sitting in a car alone or walk alone or seems lost or if the child is in any situation that may pose danger to him/her, be a more concerned society member by going to the child. It will be good if you are able to start a conversation with the child but if you are not, do not walk away. Be with the child until his/her parents come to him/her or try to alert the authority. By that we mean to include security guard if that happens in a shopping mall.
If the child is trapped in a car, alert the authority while pursuading the child to unlock the door. It is important to alert the authority so that your action will not be misunderstood by others. If the child refuses to unlock the door, do not walk away but stay there until his/her parents comes or the authority reaches the place.
Your decision to stay/keep an eye on the child may save him/her as someone else may be watching and waiting to strike. That someone may be a child predator.