My 6 year old DD has a couple of times come to me when her and my 3 year old DS have been playing in a different room, and told me my DS has hit her. Now this is possible, he has been going through a phase of being quite physical and rough recently with her and we are trying to really crack down on this with firm, clear consequences. However, I have observed a few times where they have been playing fine and he has maybe stumbled into her or picked something up and accidentally knocked her with it and she's dramatically shouted that he hit her. So it's also perfectly plausible that he hasn't hit her.
Obviously if he has hit her I want to ensure there are consequences as he really needs to learn we won't tolerate this. But if he hasn't hit her I don't want him to get a consequence when he hasn't actually done anything. I find it hard to get much sense out of him about what has happened, and I don't want to turn it into a "he said, she said" situation anyway.
For information, normally the consequence for hitting where I witness it is I remove him from the playing and he has to sit on the sofa and have a bit of quiet time away from the game. After a few minutes, I remind him how to be kind, and what words he could use instead of hitting, e.g. "Please can I have a turn after you." and then encourage (but not force) him to apologize.
So what do you do if one child tells you another one has hit/kicked/bitten them but you aren't sure of the reality of what has happened.