My boys are what were once called Irish Twins; that is, I had them less than two years apart and far too close together for most people’s comfort. . . . I did this because I had a deep and enduring belief that two children born less than two years apart would become boon companions and lifelong friends, despite all the evidence -I’d seen to the contrary. But this is indeed what happened. Quin could not remember life before Christopher, and Christopher had never had a life without Quin. -- Anna Quindlen, Siblings

Strategy four in preventing sibling rivalry calls for a look at age spacing between children. What age difference works best for dampening jealousy and, even more important, cultivating friendship between siblings?

Couples consider a variety of issues in the process of deciding when to have a second child. Besides factoring in a mother’s health and family finances, parents think about the emotional impact a second child will have on a firstborn child. Parenting experts have contributed to this aspect of the decision-making process by offering views on what they consider ideal spacing between children. In recent years, widened age differences have become increasingly popular. It is now common to hear psychiatrists, psychologists and physicians advise gaps of three to four years between births. These child experts base their recommendations on several considerations, many of which are set on some shaky ground.