If it’s 100 degrees and your kids are swimming, playing with water toys and in the shade, going outside is perfectly fine if you are keeping a close eye on them. However, If they are running around in direct sunlight, a lot of kids will overheat — even if the temperature is just in the 80s and doesn’t feel quite as hot, says Posner. A good rule of thumb is, If it’s too hot for you, it’s too hot for your kids, Dr. S. Daniel Ganjian, a pediatrician at John’s Health Center in Santa Monica, California, tells SheKnows. When the heat index is 100 degrees or more (over 90 degrees with 60 percent humidity), heat exhaustion is much more probable without safety measures taken, Hoff tells SheKnows. Younger children are more susceptible to heat exhaustion because they produce less sweat and are less likely to feel and understand the dangers of extreme heat, Hoff says. Age does matter, Babies and toddlers’ bodies don’t have as advanced heat regulation as adults’ bodies, according to Stony Brook University Research.