sibling rivalry

I have a five-year-old granddaughter and 8-year-old grandson who pick and fight constantly, well, occasionally they do play nice together. When they start, I just separate them and make them play in different rooms. I tell them if they can't play nice together they can't be together at all. It drives them nuts! As much as they fight, they can't stand to be apart! I would do the same with your two, except being toddlers they need supervised and you can't be in two places at once. It could be that he is just needs a little more individual time with mom; if he is the older one then he probably feels he is being replaced in your heart.