Acknowledge jealousy as a real and understandable emotion, but one that must be handled within limits and household rules.
Parents will do well to practice prevention with siblings, reinforcing cooperation in general and any specific examples of good deeds performed on behalf of each other with acknowledgment or even rewards if the rivalry is serious.
Advise parents to be sensitive to situations, like boredom, that lend themselves to sibling disputes, and to intervene with distractions. Promote cooperative projects and noncompetitive games: building a fort or puzzle, playing in the sprinkler, or making breakfast as a family, instead of games with winners and losers.
When board games are necessarily competitive, make it a practice to turn the board around every fourth move to minimize age-related inequities. Even out the teams in driveway basketball as well.
Once children are old enough to participate, family meetings are an excellent forum in which to air grievances. Again, ground rules apply; everyone gets to be heard. No interrupting. Solutions can be brainstormed and tried out, to be reviewed at the next regularly scheduled session.
A stepwise approach to dealing with actual sibling disputes also helps bring order to the chaos that feeds sibling wars. Parents may want to read the popular if optimistically titled book by Adele Faber and Irene Mazlish, “Siblings Without Rivalry” (New York: HarperCollins Publishing, 2004).
Essentially, their basic plan is to teach parents to ignore whatever can be ignored, thus avoiding a self-feeding loop of inadvertent reinforcement of the conflicts.
Situations that are a bit too much to ignore should be handled dispassionately. The parent may want to ask, “Is this a real fight or a play fight?” If it's a play fight but noisy, they might want to suggest a new venue—in the basement or outdoors.
If it's a real fight, encourage parents to simply describe the situation they see. “It looks like you both want to play with the truck, and it's hard to decide how to work it out.” Follow this with an affirming statement like, “I'm sure you can figure out a solution.”
If things are even more volatile—maybe someone has hit or pinched—parents should intervene, but in an unbiased manner and with the least amount of punishment that makes sense. They need to emphasize that hitting is never acceptable, but not take sides. A useful mantra for parents: “Don't try to judge who started it. You can never tell.”
Depending on the situation, both children may need to be sent to a room away from the toy to make a plan for resolution. The toy may need to be put in time out. Both kids may need to be put in time out for the same amount of time, with duration based on the younger child's age. Each child may need to take on an individual chore card, or even chores requiring the effort of both kids.
Whatever the solution, it should be brief.
Counsel parents that rivalry is part of sibling interaction: a challenge best met through prevention, structured responses, and reliance on family rules.
Remind them of the fleeting nature of sibling spats—don't they hear the kids giggling 15 minutes later?—and the permanence of warm, mutually respectful, sibling bonds through a lifetime.