Is a large family a protective factor against behavioural and emotional problems at the age of 8 years?

Aim: To study the prevalence of behavioural and emotional problems among children from different family types, sibship size and birth order. Methods: A prospective birth cohort (n = 9357) study where parents filled in two questionnaires and teachers assessed children's behaviour using the Rutter scale (RB2). Results: 14.3% scored above the cut-off point (RB2 greater than or equal to 9) indicating probable psychiatric disturbance, boys more often than girls (OR 2.6, 95% CI 2.3-3.0). Behavioural problems (9.2%) were more common than emotional ones (4.1%). Boys living in families other than two-parent families were at risk for probable psychiatric disturbance, and a corresponding risk was observed for girls living in single-parent or always one-parent families. Other than two-parent family was also a risk for behavioural problems; for boys adjusted odds ratios ranged significantly from 1.8 to 2.4 and for girls from 2.0 to 3.7. "Only children" had the highest prevalence of behavioural problems, while children in very large families had the lowest. Living in a very large family was a protective factor against behavioural problems among boys but not among girls. Eldest children were at lower risk of behavioural problems than the other children. The single-parent and always one-parent family was associated with higher risk of emotional problems among girls. Conclusion: Children's psychiatric problems are manifested at school mostly as behavioural problems. A two-parent family and being the oldest in the sibling series seem to be protective factors. Very large family size, if not connected to social disadvantages, does not seem to be a risk factor for children's behaviour.