Infants, toddlers and young children need outdoor activity to build strong bodies and minds, but they also require extra care in the heat. In the summer months, those twin imperatives can make parents anxious. How long should kids be out? How do I know they’re OK? What should I avoid?Human-caused climate change is making heat waves longer, stronger and more widespread. Much of the U.S. sweltered last week under a heat dome.That shift makes questions about keeping babies safe more pressing, said Dr. Katherine Williamson, a pediatrician with Rady Children’s Health in Orange, California.“We talk about drowning and choking with…