CHICAGO — The toddler announced she was “going to be brave” shortly before the needle pierced the fleshy part of her right thigh. Although her big brown eyes widened a bit at the sight of the syringe, she held onto her mother’s hands and looked away, managing not to cry or whimper the entire time. Afterward, the little girl proudly showed off the cartoon Tweety bird adhesive bandage placed at the injection site. “You did so good,” her mom said, embracing her daughter’s tiny frame before discussing milkshake flavors, the treat of choice after getting the shot. Three-year-old Elena Rosales is a ...