Four-year-old katie observed charlotte, two years younger, begin to cry when she fell down. katie immediately ran over to charlotte and patted her on the back and told her everything would be alright. she even began to cry herself. katie's ability to infer charlotte's mental and emotional state is an example of:

The answer to this question is theory of mind
theory of mind refers to the ability to form belief and perception based on what we observe subjectively.
In this particular case, when katie observe what happen to charlotte, she formed the perception that Charlotte is hurting need help and comfort so Katie instictively ran to Charlotte to give them.