My 3-year-old hugs too hard and doesn't like loud noises. What could be causing this?

There are a lot of things that could be causing this behavior. It could be that your daughter’s intention is to comfort the crying girl because she knows that hugging is the way to comfort someone, but then she goes overboard. She might not understand the limits of how much you should hug and how much you back off. Some kids are more awkward in the way they give comfort, and actually need to be taught what is an appropriate hug and how much space other people should have. It could also be that your daughter doesn’t have a good awareness of her body in space, and struggles with controlling her gross motor skills. It may also be that what started out as a gesture to comfort another child turns into a sensory-seeking, and socially inappropriate, behavior.

You say she also seems to react strongly to loud noises like sirens, trains, and crying. While many kids have hyper- or hypo-sensitivities to sensory stimuli, and in particular are averse to loud sounds, it could also be a sign of a developmental issue and may warrant a deeper look by a specialist.

Your daughter isn’t too young to be diagnosed with a developmental problem, and there are actually a lot of reliable ways to assess developmental challenges in children even younger than her. Considering the two behaviors that you’ve described, I recommend getting an evaluation with a clinical psychologist or a neuropsychologist who understands early childhood development and is familiar with preschool assessments.