Little tolerance for heat

Eliza loves to play outside and she gets quite upset if I try to let Amanda and Caitlyn go out to play without her. She immediately goes to get her shoes and brings them to me to put on. This week she's even started going automatically to get her shoes after she gets down from lunch, since that is the time we usually go outside. I have discovered, however, that she has very little tolerance for the heat. Since the weather has gotten warmer, she doesn't want to play anywhere except in the shade. So she's been spending a lot of time in her swing out front.