Even those parents who keep a close eye on their children sometimes get distracted enough that their child wanders off and gets lost.
To ensure children can let parents know where they are upon becoming lost, have them wear a safety whistle, attached to a lanyard, around their neck. Tell the child in advance that should they become lost to simply blow on the whistle. The sound of a whistle will travel farther than a shout.
Consider including an ID card on the lanyard, especially if the child is a preschooler or of very young elementary school age. In case the lost child is injured but then found by others, the ID card can be useful in providing important medical information.
The ID card should include the child’s name and date of birth, the parents’ names and their contact information (especially a telephone number), blood type, and any allergies.
Read more about day hiking with children in my guidebook Hikes with Tykes.