The older child who responded to the news of a new baby with delight may now be hitting the baby, refusing to eat, and wetting the bed again at 3.5 years. This is not a failure of preparation or parenting; it is the developmental and emotional reality of what it means to share your world with a new person who arrived without your consent. Understanding this as a normal response – and knowing what actually helps – makes a significant difference to both children and parents.
Healthbooq (healthbooq.com/apps/healthbooq-kids) covers family transitions and sibling relationships in the early years.
Why the Adjustment Is Hard
Before the baby arrived, the older child had the parents' full attention. This is not just an emotional comfort; it represents the entire world as they know it. Judy Dunn at King's College London, whose longitudinal research on sibling relationships and their long-term developmental significance is foundational, documented that the arrival of a new sibling involves a genuine and significant loss for the older child – loss of exclusive parental attention, loss of the established family order, and loss of a certainty that they are the primary focus of parental care.
This loss is experienced differently depending on the child's age. For children under 2, the conceptual understanding of what is happening is limited, but the change in parental availability is felt directly. For children between 2 and 4, the cognitive awareness of the displacement is clearer and can produce more intense and deliberate responses. For children aged 4-5, there is more capacity to understand the meaning of a sibling relationship and to engage with it.
Regression: Understanding the Backwards Steps
Regression – returning to behaviours associated with an earlier developmental stage – is one of the most common and most alarming responses for parents to witness. A child who was reliably dry begins wetting again; a child who fell asleep independently begins needing to be rocked; a child who spoke in sentences reverts to babbling; a child who had dropped their dummy asks for it back.
These regressions are emotional communications, not failures of development. They often reflect a blend of stress response (cortisol elevation associated with significant change) and a desire to return to a time when things were simpler. Some children also pick up, consciously or unconsciously, that the baby receives a great deal of care when very young, and may identify baby behaviours as a route to care.
Responding to regression with patience rather than frustration, and providing warmth, tends to shorten its duration. Increasing the older child's access to positive parental attention during this period is often enough to resolve the regression.
What Helps
One-to-one time. Research by Frank Sulloway at the University of California Berkeley, whose work on birth order and sibling dynamics is widely cited, and by Dunn, consistently documents that the quality and quantity of individual parental attention is a critical buffer against sibling jealousy. Even 15-20 minutes of fully focused, child-directed one-to-one time daily makes a measurable difference.
Meaningful involvement. Involving the older child in the baby's care – fetching a nappy, singing to the baby, helping with bath time – reframes the baby from a competitor for parental attention to a project the older child is invested in. This sense of importance and contribution reduces rivalry.
Acknowledging mixed feelings. Telling a child who is hitting the baby that they are naughty does less good than acknowledging the feeling: "I can see you are really angry. You don't like it when I have to stop our game to feed the baby. That's understandable. Hitting hurts the baby and we're not going to do that – but you can tell me how you feel." This approach, drawn from the emotion coaching research of John Gottman at the University of Washington, validates the child's experience while maintaining firm limits on harmful behaviour.
Preparation before the birth. Books about becoming a big sibling, talking about the baby as a real person who will have a relationship with the older child, and visiting other families with babies all help. Involving the older child in choosing a few items for the baby gives them a stake in the baby's life before it arrives. Crucially: don't oversell how wonderful a sibling will be, or the disappointment when the baby is boring and demanding will be sharper.
The Timeline
Most sibling adjustment research documents that the most intense adjustment period is in the first 3-6 months after the baby arrives. Most families report that by the baby's first birthday, the older child's relationship with the baby has become a genuine and positive relationship, with the older child often playing a protective and nurturing role.
Key Takeaways
The arrival of a new sibling is one of the most significant family changes a young child experiences. Regression – a return to earlier behaviours such as thumb sucking, bedwetting, tantrums, or baby talk – is an extremely common response in 1-4 year olds and represents the child's emotional reaction to change rather than a developmental problem. Dedicated one-to-one time with the older child, involving them meaningfully in baby care, and acknowledging their mixed feelings directly are the most consistently supported strategies. The adjustment period typically takes weeks to months; most children ultimately benefit significantly from having a sibling.
