Info from "A Guide to the Nests, Eggs, and Nestlings of North American Birds":
"...Bill pinkish-gray, becoming yellow. Mouth pale orange. Legs and feet gray, becoming greenish-yellow. Iris pale gray to white."
All chicks in photos are probably little blue herons. The book description for black crowned or snowy egret hatchlings does not match your photos. (No photo or color plate available in this book.)
ASM Fall Meeting: September 27-29, 2019 at Camp Clover Point, Lake of the Ozarks State Park, Osage Beach, MO Details and Online Registration