If the gap is less between the two children of a couple, bringing them up is a very uphill task these days. In the olden days, the story is different. Those days parents used to think that their children are also like the other children and they never bothered to bring them up like the son of a King. So the parents never felt the pain. But now no parent is going for more than two children. They feel that their children should not suffer and they should not face any problem and they want every luxury to be available. In this process, only the parents feel a big problem.
In my opinion, a gap of 3 years between two children of a couple is good enough. The main criteria should be that their children should settle in their lives by the time the parents reach their retirement age. Yes. Initially, for 2 or 3 years the mother may suffer due to competition between the two children. But once both of them start going to school, they will become more friendly parents may not have many difficulties in bringing them up.