P.G.
Let them figure it out for themselves. Sometimes we parents feel we have to step in to ALL disagreements with our kids, well, we don't!
Next time they start in, just look at them and walk away and as you are walking away--tell them; "Oh, just figure it out!" or; "Deal with it!" they will soon see that mom is not going to pick sides, step in, or get all flustered about their little tiffs and they will either leave each other alone or they will get along or Heck they might even fight more...who knows it is all trail and error.