Carrying a mobile phone always is a good idea one in case you need to make an emergency phone call. If possible, you always should call a responsible party to let them know when you’ve arrived at your trailhead. Be aware that a mobile phone may not have reception in many remote areas. In addition, there probably is no way to recharge your phone other than through your vehicle, so take care of that before leaving home.
Also, remember that you’re on a nature trail, not a city sidewalk. As Mark P., of Rapid City, S.D., notes, “When on the trail, put away the mobile phone. The object of the adventure is to spend time with your kids and to enjoy nature. Use it only for emergencies. If you must take a phone call on the trail, be discrete as other hikers may hear your conversations.”
Read more about day hiking with children in my Hikes with Tykes guidebooks.