The birth of a baby is an event that will bring change to all members of the family, and as such may be a stress-inducing factor. In fact on the Holmes and Rahe (1967) Life Change Index pregnancy is rated as 40 stress points, which in isolation may not be much, but as stress is cumulative, it is easy to see it as a major contributory determinant. It is common for a mother to begin to overreact to what once were considered minor annoyances, begin crying for no apparent reason and even begin to resent the new member of the family. This condition is known as post-natal depression or post-partum depression and according to some research affects the majority of new mothers. Some of the sharpest effects of this post-partum depression will manifest themselves in, what is currently termed, abuse, on the new-born infant.

Emotional deprivation, too, cannot be overlooked as a contributory factor as inducing stress in the child. Some research has concluded that any breakdown in the mother-child relationship could cause severe emotional, intellectual and social consequences. The idea of an infant's and a young child's need for unconditional love and concern is further advanced by the Newsons (1976) when they say '...the developing personality needs to know that to someone it matters more than other children; that someone will go to unreasonable lengths...for its sake'. Perhaps this is more in line with the current psychological view that mothers need not be the sole care-givers, but as long as there are not too many and that each gives the child the love and care and stimulation, the stresses imposed on the baby or infant will be minimal.

When a new baby is born, there may be stress placed on any young children at home. They may feel a sense of loss as this could be the first time that the mother has been away from home for any length of time. Where a child is made aware that mother has gone into hospital this may bring on feelings of fear and anxiety, especially in cases where the child associates hospitals with death and disease. There may be emotional scenes when mother and new baby do come home; older children may feel threatened and therefore placed in potentially stressful situations by the attention parents may devote to siblings.

When the focus of attention has become the new baby it is not unknown for sibling rivalry to manifest itself in the form of aggressive behaviour towards the intruder, with, for example, bites being substituted for kisses and objects that could harm being placed near the rival. In some instances, the method of coping with the stress is that of regression, a term used to describe a condition where an individual who is under stress reverts temporarily to a more immature state. In the young child, this is typically shown by a reversion to babyish behaviour, talking baby talk, crawling or bed-wetting for the first time in months. Psychologists do not consider this to be harmful as a coping mechanism as long as children return to age-appropriate behaviour when they have adjusted to the stress. It has been suggested that some emotional envy and jealousy is inevitable when a new baby is born as far as older siblings are concerned. The nature of this stress can be minimised by parents taking the older brother or sister to visit their new baby in hospital and be present at gift-givings and be encouraged to become involved in the upbringing of the new child.