At Wave 1, the newborns were approximately 2 months old. The mothers participated in an in-home interview and completed questionnaires about some aspects of their family life, affection and conflict between siblings, shared and different experiences of siblings as they grow up, how parents taught children new skills, cooperation within relationships and conflict resolution. Information was also collected about socio-demographic characteristics, child behavior, childcare and neighbourhood.

Cheek swabs were also collected.

At Wave 2, the children were on average 18 months old. Data collection included questionnaires about family and neighbourhood.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Cheek swabs were also collected.

At Wave 3, the children were on average 3 years old. Data collection included questionnaires about family and neighbourhood.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Cheek swabs were also collected.

At Wave 4, the children were on average 4.5 years old. Data collection included questionnaires about family and neighbourhood.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Cheek swabs were also collected.

At Wave 1, the newborns were approximately 2 months old. The mothers participated in an in-home interview and completed questionnaires about some aspects of their family life, affection and conflict between siblings, shared and different experiences of siblings as they grow up, how parents taught children new skills, cooperation within relationships and conflict resolution. Information was also collected about socio-demographic characteristics, child behavior, childcare and neighbourhood.

Characteristics of the children including temperament (children’s emotional reactions when a game is played with them), language (vocabulary development), children’s understanding of other people’s thoughts and feelings, and stress reactivity in childcare environment were observed.

Physical measures were taken including height, weight and gestational age at birth.

Saliva and cheek swabs were also collected.

At Wave 2, the children were on average 18 months old. Data collection included questionnaires about family and neighbourhood.

Characteristics of the children including temperament (children’s emotional reactions when a game is played with them), language (vocabulary and reading skills), executive functions (inhibition, flexibility, emotional control, planning and organisation, self-monitoring), children’s understanding of other people’s thoughts and feelings, and stress reactivity in childcare environment were observed.

The relationships with siblings and peers of the children were studied. Cognitive sensitivity, internalizing behaviours (depression, anxiety, substance abuse, eating disorders, etc), and externalizing behaviours (physical and verbal aggression, bullying, vandalism, etc) were evaluated.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Physical measures were taken and included height and weight.

Cheek swabs were also collected.

At Wave 3, the children were on average 3 years old. Data collection included questionnaires about family and neighbourhood.

Characteristics of the children including temperament (children’s emotional reactions when a game is played with them), language (vocabulary and reading skills), executive functions (inhibition, flexibility, emotional control, planning and organisation, self-monitoring), children’s understanding of other people’s thoughts and feelings, and stress reactivity in childcare environment were observed.

The relationships with siblings and peers of the children were studied. Cognitive sensitivity, internalizing behaviours (depression, anxiety, substance abuse, eating disorders, etc), and externalizing behaviours (physical and verbal aggression, bullying, vandalism, etc) were evaluated.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Physical measures were taken and included height and weight.

Cheek swabs were also collected.

At Wave 4, the children were on average 4.5 years old. Data collection included questionnaires about family and neighbourhood.

Characteristics of the children including temperament (children’s emotional reactions when a game is played with them), language (vocabulary and reading skills), executive functions (inhibition, flexibility, emotional control, planning and organisation, self-monitoring), children’s understanding of other people’s thoughts and feelings, and stress reactivity in childcare environment were observed.

The relationships with siblings and peers of the children were studied. Cognitive sensitivity, internalizing behaviours (depression, anxiety, substance abuse, eating disorders, etc), and externalizing behaviours (physical and verbal aggression, bullying, vandalism, etc) were evaluated.

Observational measures of mother–child interactions were taken evaluating the level of responsive parenting (emotional availability and response to the child in a way that is appropriate for the child’s needs) and the level of differential parenting (different treatment between siblings).

Physical measures were taken and included height and weight.

Cheek swabs were also collected.