It's easy to have crop infections in young ones. Besides the advice above, your second picture of poops shows one with very green urates. This can be from an infection. It can also happen if they aren't getting enough food as in baby bird formula.
Little ones can go down hill so fast. Very much recommend getting them quickly to the veterinarian. Often with veterinarian prescription they can quickly recover. Delay in seeking veterinarian can lead to death.