Some children might be a little more klutzy, which would be a concern if the rabbit is near. Rabbits like to running in circles around your feet, they move around quickly and without realizing they could even trip you by mistake. This is both dangerous to your child and the rabbit. Making sure to supervise when they are around the rabbits will help make sure everyone stays safe.
Any loud noises would be scary to a rabbit. This could be stomping, things dropping/thrown on the floor, electronics, toys/games, raised voices, etc.
Fast movements can mimic a predator, this would be quite frightening to a rabbit and makes them feel like their life is in danger. We would want to be mindful of any running, jump, throwing, etc.
Being prey animals they don't want to feel confined or like they can't escape to safety. Not feeling like they can be safe or go somewhere to be able to feel safe will cause anxiety, stress, and is scary to a rabbit. Anytime they are trying to get away while being held, kept somewhere they aren't familiar with, kept away from where their area is, etc they will feel this way.