Few things can grate on a mom's nerves like constant fighting. You want your kids to be best friends with each other, to play well together, and to love each other, but you may be at a loss as to how to deal with the inevitable bickering.
The first step to dealing with a fight is to help your kids calm down. When emotions are running high, kids are not capable of problem solving. You may need to separate the children, not as a punishment, but as a break to help each one regain some equilibrium. Do you know what calms your children down? Is it being alone or cuddling with you? Do they feel better when they sit down with a book or doll or when they listen to music? Does it help them to have a comfort item? If you ask your children to take a break in their rooms, tell them what they can do ("You may sit in your beanbag and talk to your doll," or "You may play with your legos.")
When the emotions have settled, talk to each child individually about what happened. Have them put their feelings and the events into words, and help them notice what upset them. Reflect and affirm their emotions. ("That must have been really frustrating when your little brother knocked down the tower you worked so hard on.")