grandson's safety

My son told me yesterday that our 2 1/2 year old grandson had used his little buffet to get a knife out of the kitchen drawer along with a block of butter and spread it up the stairs and along the wall. My son found it amusing. Mum was upstairs at he time. I didn't find it amusing but very worrying. He should not be left in a position to get a knife. Mum was obviously upstairs quite a while and also oblivious of what he was doing. I didn't comment of my thoughts to my son. This is not the first time he has told me things like this. They also have a 11 month old baby as well.