Q: My husband and I have one child, age 2. We’d like to have at least one more. What is the optimal spacing between children? A: Research puts ideal sibling spacing at three to four years. A child 3 or younger may respond to the birth of a sibling by regressing behaviorally and even becoming aggressive toward the new arrival. On the other hand, a child who is an “only” until age 4 may have difficulty giving up the benefits of that status. In either case, the risk is greater of ongoing jealousy on the part of the older child. Whereas there are no guarantees in childrearing, only probabilities, …