What is the optimum age gap between children? Will a short gap incite furious sibling rivalry, or a long one risk your children never becoming friends? It's a tricky parental conundrum - and one where people are apparently happy to offer opinions, but not absolutes.

“We know the general effect of age gaps, but family dynamics change things so there are no guarantees,” says Dr Richard Woolfson, a child psychologist and author of Understanding Children. “However, sibling rivalry tends to be at its strongest when the age gap is around two years. It's less intense when the first child is 18 months or younger and the second child is born because they don't have a fully developed sense of identity. While after three years it's also lessened because the older child will have more of a sense of independence and feel more secure in their own life.” And these initial feelings of rivalry can haunt your children if they aren't dealt with when they are young.

Working out what is right

Is there any research into what is the “right” or optimum gap? According to the Office for National Statistics, the average interval between births (for married women in England and Wales) is 35 months, a sensible interval if you're trying to minimise sibling rivalry. This almost three-year gap could also be wise when it comes to maternal health. Research by the Catalyst Consortium, a US government-funded organisation that works to reduce maternal, infant and child mortality worldwide, suggests that it is near to optimum for health reasons.

Much of its data was based on the developing world, which has much higher rates of infant and maternal mortality. However, experts here agree that it makes sense to let the body recover from one gruelling pregnancy and childbirth before moving on to another one.

A further study from the Centre of Population Studies at the School of Hygiene and Tropical Medicine in London, supports this. It discovered that women in developed countries who wait less than 18 months between having children are more likely to die young than those who have a bigger gap. By the age of 50, the death rate for those women in their study was 20 per cent higher than those with a larger sibling gap.

Shelley Lief and her husband Kevin have a seemingly perfect gap between their two sons, Alex, 6, and Jacob, 3. And another little brother has been born almost exactly three years later. “We didn't think we could cope!” says Lief, 37, as she explains why they went for that interval between the boys.

“We didn't sit down and plan a three-year gap, and there was definite peer pressure to go for two or two-and-a-half years, but I didn't want a toddler and a baby. I wanted an older child who was a bit more independent, but not so much older that he wouldn't be friends with his new sibling. I knew I didn't want a tiny gap; that's very hard on the parents. “The two boys are very close and play together all the time. I don't know if it's an optimum gap but it works for us.”

Professor Judy Dunn, a developmental psychologist and expert in child development, agrees that this three-year interval may be a good one. “It's true that there are big differences in how a first-born reacts to a new baby, depending on how old they are,” she says. “A two-year-old will show upset in a very different way from a five-year-old, and if a child can talk, lots of things are different.

“You can amuse and distract a verbally precocious three-year-old when you are with a young baby. That's harder with an 18-month-old. By 3, most first-born children are amenable to pressure not to beat up the baby. But how well siblings get along is very dependent on the older child's temperament.” Lief also believes that gender made a positive difference. “I knew nothing about boys before,” she says. “But they have got so much in common, from superheroes to play-fighting. I'm sure it makes them closer.”

“Everyone's experience is different”

Gender may well play a part, but it's debatable whether this is good or bad. Many women who get along just perfectly with their little sisters as babies (all that sharing of pink tutus) find that this sharing turns into competitiveness as they grow up and are compared more easily than siblings of opposite sexes. The same goes for those Spider-Man playing brothers. “Everyone's experience is different” says Dr Woolfson. “The kids may get along fine when they are 4 and 2 or 8 and 6, but the gap can seem vast when they reach 13 and 11, whatever their gender.”

Professor Dunn says: “If you're interested in a child's wellbeing, in a psychological and emotional sense, they can do very well with a five or six-year gap, or a year between them. If you're worried about the quality of the relationship between your children, you're right, it will be very different depending on whether the gap is small or big, but there's no simple equation.”

There is also the question of intellectual development, as it is suggested that this is helped by a larger gap. Language development in particular improves when a child spends more time with adults rather than siblings of a similar age. However, once again, there are many other factors at play when it comes to intelligence.

“Every age gap brings strengths and weak-nesses,” says Dr Woolfson. “I would strongly discourage any parents from choosing an age gap on the basis of reducing tension between children or how intelligent they want their child to be.” And whatever the age gap, parents need to prepare children carefully for any new arrivals, or face dire consequences. How siblings get on may owe more to personality than age, but parents can make a real difference. “If it's not resolved in childhood, then the impact of age gaps will continue into adulthood,” warns Dr Woolfson. “Parents need to be aware of this and make every effort to work at it with the children, encourage them to get on and make each of them feel special.”

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