Ever since we started going on day hikes, I have always had my children carry their own day pack with a water bottle, spare clothing, snack/lunch and a whistle. This gives them a sense of responsibility for meeting their own needs. If either one of them were to get seperated they would at least have some basic necessities with them. To prevent anyone getting separated we have a simple rule; If you can't see anyone behind you if you are in front then you need to stop and wait. What do you do on the trail to keep your kids safe yet allowing them some freedom?