When they reached the ER, Cas simply hung back and watched the Doctor with interest as he interacted with the child. Children were something he'd found he liked. They were easier to speak with than most adults, even if their behaviour was often more nonsensical than that of their fully grown counterparts. There were many actions she could have taken to prevent having broken the arm and yet she'd not thought of any of them. To someone who had never been a child, this made little sense.
"I fell," she said simply. "You don't look like the doctor who was here before."
The child was strangely more observant than the adults of the world they were currently in, but that left him to wondering as to whether or not it was simply the adults who were abnormal in their thoughts and behaviors. "That's because he's a better doctor," Cas said simply. "This one knows more than the other."
"Oh," the little girl replied. "You can fix my arm?"
Cas understood that the Doctor potentially disliked him speaking up, but he'd said what he needed to. The other man could continue from there. It was already evident that they'd won the little girl's trust and that was all they'd needed for the moment.