I feel like one major influencing factor that could help determine a child's attachment would be the presence of a sibling. If a sibling, especially in relatively young children, is present, I would assume that the children would fight for the attention of one parent or another, thus creating either a more secure attachment to one parent over another, or maybe even resentment and an anxious/resistent or anxious/avoidant relationship with one or both parents. Alternatively, if the sibling is significantly older, the young child may form a secure attachment to the older sibling in leiu of or along with forming secure attachments to parents.
