I see this mistake happen constantly – a parent is watching their kid (who is just learning how to walk) run straight into a table that is conveniently right at head height. The kid then looks around for mom (or whoever), not quite crying yet but definitely on the brink of tears, and the mom instinctively freaks out and puts on a horrified face to match. The kid begins to cry hysterically as a reaction to seeing the mother’s face.
For the most part, this can be avoided by smiling and not over-reacting when your kid looks to you for guidance. For one thing, they are confused. They haven’t felt like this before (they could be one or two years old) and they know what just happened is a bad thing but aren’t quite sure yet how to process it. They start looking around for guidance to see how others are reacting to the situation. So when you smile you are re-assuring them that everything is going to be OK. If you don’t panic then they won’t panic. Pretty much every single time something like this happens the kid will calm down almost immediately in response to a calm face/demeanor and genuine smile. When they see you happy and calm, they get happy and calm. If the kid is really hurt then they will be inconsolable and you will just know (i.e., the crying is almost instant).
When I worked as a day care teacher I would sometimes say things like, “Oh, no! Is the floor OK?” and rub the spot on the floor where the child was hurt. They would become concerned over the floor’s well-being instead of reacting about their own. I remember one toddler even apologized to it.
It can also help to lay some infant-directed speech at them during a situation like this. But, ultimately, they’re just looking for facial confirmation that they’re not going to die. Of course you’re still going to want to check them over for any serious bumps or bruises but just make sure you’re smiling when you do it.