Babies should sleep in their mother's bed until they are at least three years old. It was claimed last night. The controversial advice comes from a paediatrician who found that two-day-old babies who were placed in cots slept less well than those who dozed on their mother's chest. Their hearts were also under more stress, it was claimed. Sleeping alone makes it harder for mother and child to bond - and damages the development of the brain, leading to bad behaviour as the child grows up, researchers fear. Dr Nils Bergman, of the University of Cape Town, South Africa, says that for optimal development, healthy newborns should sleep on their mother's chest for the first few weeks. After that, they should stay in the mother's bed until they are three or even four years old. However, studies linking bed-sharing with an increased risk of cot death and fears that a mother will roll over and smother her child means that women are generally advised against this. In a recent British study of sudden infant deaths, almost 2/3 of those that were unexplained occurred when the bed was being shared. But Dr Bergman said: "When babies are smothered and suffer cot deaths, it is not because their mother is present. It is because of other things: toxic fumes, cigarettes, alcohol, big pillows and dangerous toys."