Foolish parents may not understand that kids does not have the ability to follow them. They will only have this cognitive ability upon reaching a certain age. All adults should understand that kids understands only that the world revolves around them, not the other way round. That is why they do things independently believing their parent will be there, and as they have short attention span, will move from one attraction to another without worrying about being lost.
Once parents recognised and understand, then what they should do is to teach them what to do in case they get lost. One is to stay where they are and call out to their parent. Another to approach an adult and give some essential information to assist the adult to locate his/her parent.
It is not uncommon for kids to get lost, but being prepared that it may happen to one's child will ensure that he/she can be found as quickly as possible.