Well, I have a preschooler and two in elementary and this story is their life. The first thing they do is argue with each other and if it is not resolved then I hear "Mo-om! So and so is doing such and such" and I come and negotiate a settlement. (In fact, they understand this concept better than many of the GROWNUPS in my congregation who tend more towards talking about the person they are mad at... but I digress.)
Drama - a drama or puppet show lifting up preschool conflicts and how they are resolved would be to the point.
Movies -- Perhaps a series of clips where characters are angry with each other. Do they solve their problems the way the scripture recommends or do they take another route?
Art / Science -- Can't paint on crayon or wax paper it rolls off. But add soap and the paint will stick. Make the analogy that the soap is like the third person that helps the wax and paint get along. Or have a lesson on colors -- how can red and yellow live together? They can be red here, yellow there or they can come together and make orange? You'd have to be creative in the lesson design to make sure they got the point.
Cooking -- You talked about bringing someone into the fold -- How about the cooking concept of folding something in? If you just stir it in, you lose the air bubbles (holy spirit) but when you fold it in, you keep the air and lightness. Sponge cake, anything with whipped cream or egg whites. This may be getting pretty abstract for preschool?
Hope this helps!