 A 10-year-old boy died last week in Phoenix after a hike on a 113-degree day. A four-month-old girl died Friday after being taken on a boat on Lake Havasu in 121-degree weather. And a two-year-old girl died Tuesday after being left in a car near Tucson when the high was 111. Dr. John McGreevey with Phoenix Children's Hospital says kids' bodies can be very vulnerable to extreme heat. So as parents, we have to be really watchful.