Please could you all tell me what age you leave 2 siblings together in the same room. I have a son of 5 and a daughter of 2. I usually don't leave them unattended but today I wandered into the bedroom to talk to by husband and left my son in my daughters room where she was in her cot. I heard them giggling so after a minute or so I went to see what they were upto I found my son using a cusion to hit my daughter over the head. She was still sort of laughing but starting to look worried and panicy when i got to them. I shouted for him to stop and asked him what he was doing. He replied a pillow fight. He said that he had knocked her back which he said she found funny. I was really alarmed that he would do this and also worried he could of her hurt her head. The cusion is quite dense. Please reasure me. We have now put a gate on her room to stop him wandering in when we are upstairs. Feel terrible.