What do you do?

Backstory-- a coworker told me about this daycare and my son has been there since 6 months old. He's 21 months now. Her older son goes there (he's 4) and her baby (8 months old) just started going there. I will admit that my son has had issues with the baby because he was the "baby" at daycare for so long.

And, today, this coworker came to my office at lunch to tell me that my son hit her baby son on the head because he thought the baby was going to take his toy. She said her older son told her (and she asked him many times to make sure he told the story straight.) I asked her if DS had a time out and the boy said no and that maybe the teacher didn't see. I told her that I literally have no idea what to do since I am not there and I FULLY support him being put in time out or having the toy taken away.

While we are friendly coworkers, I really wish she had talked to the daycare provider to get the full story first (she hasn't talked to her.) I told her that I don't want to put the onus on a 4 year old, but if her older son ever sees something like that again to immediately tell the DCP.

It was so awkward and was trying so so hard to not tear up.

What do I do now? DS is too little to talk about it with and I am not there to regulate him...

(Sorry this is rambly and maybe I didn't handle it the best but I was blind-sighted. )