Very few things in a young child's life match the disruption of a new sibling. The child who was at the centre of the family's attention discovers, overnight, that there is a new presence who cries loudly, gets fed constantly, is held by everyone, and never seems to go away. The parents are different – more tired, more distracted, less available. The world the first child knew has changed in ways they did not choose and cannot undo.
The jealousy that follows is not a character flaw. It is a reasonable response to a genuine loss: the loss of undivided parental attention, and with it some of the security that undivided attention provided. Understanding this – rather than treating the jealousy as a behaviour to be stopped – is the starting point for managing it well.
Healthbooq (healthbooq.com/apps/healthbooq-kids) covers family transitions and sibling relationships.
What Jealousy Looks Like
Toddlers and young children express jealousy in varied ways, not all of which are immediately recognisable as jealousy. Direct aggression toward the baby – hitting, pinching, "accidentally" bumping the baby – is the most alarming and the most obvious. But jealousy also presents as: regression (bedwetting in a child who was dry; returning to thumb-sucking, baby talk, or wanting a dummy); clingy, demanding behaviour that is out of character; sleep disturbances; increased tantrums; and sometimes withdrawal or sadness that can look like depression.
Judy Dunn and Carol Kendrick's observational study at the University of Cambridge (published in 1982 and an enduring contribution to developmental psychology) followed first-born children through the birth of a sibling, documenting the range of responses and tracking them over time. Their finding that ambivalence – love and hostility simultaneously – is the normal state of the sibling relationship from the start, rather than something that develops after a period of hostility, has shaped how professionals think about sibling dynamics.
Regression is particularly worth understanding because parents often mishandle it. A 3-year-old who asks for a bottle, begins wetting themselves, or starts talking in a baby voice is communicating something rather than deliberately being difficult. The most effective response is giving the child the regression without making it a competition with the baby: "Of course you can have a cuddle on my lap, let me put the baby down for a minute." The regression typically passes more quickly when it is met without alarm.
Before the Baby Comes
Preparation before birth is genuinely useful. Explaining the pregnancy to young children from early enough that the news has time to settle; involving them in preparation; explaining honestly (and age-appropriately) what a newborn is actually like – that it sleeps a lot, cries a lot, cannot play, and will need a great deal of attention. The unrealistic expectation that a sibling will be an instant playmate, set up by enthusiastic framing of the pregnancy, sets children up for a particularly sharp disappointment.
Many families arrange for the older child to have a gift from the new baby when they first meet in hospital – a small present, as if from the baby. It is a small gesture but one that many families find effective for softening the first meeting.
During the Newborn Period
The advice to give the older child "special time" is correct but often interpreted too narrowly. It is not about quantity – it is about quality and exclusivity. Ten minutes of reading together after the baby is asleep, where the older child has an adult who is fully present and not simultaneously managing another person, can be more valuable than two hours of divided attention.
Naming what the older child is feeling – "I think you might be feeling a bit left out right now" – is more useful than either denying the feeling ("You love your baby sister!") or reinforcing the behaviour as effective ("You don't need to hit her to get my attention").
Fathers and other co-parents often have a particular role in this period: the older child may be less jealous of their relationship with the co-parent (who has not been hijacked by a new infant in the same way) and the co-parent can provide intensive attention while the breastfeeding parent is otherwise occupied.
Handling Aggression Toward the Baby
Aggression toward the baby requires immediate, calm intervention: physically preventing the hit or pinch, naming what was happening, and explaining briefly why it cannot happen. Not a major lecture; not dramatic distress. The response should neither terrify the older child nor reward the aggression with intense attention. "I know you're angry, but I won't let you hurt the baby" is sufficient.
The baby should never be left alone with a young child who has shown aggression toward them, regardless of how temporary this seems.
The Long View
Judy Dunn's longitudinal research showed something hopeful: sibling relationships, even those that begin with significant jealousy and conflict, are characterised by both great hostility and genuine closeness from very early on. The same child who hits the baby will, within weeks, also comfort the baby, make faces to make them smile, and show a specific and tender attention. The rivalry and the relationship develop simultaneously.
Research by Laurie Kramer at the University of Illinois has documented that the quality of the sibling relationship in childhood predicts warmth in the adult sibling relationship. The investment made in supporting a healthy sibling relationship through the jealousy of infancy pays off over decades.
Key Takeaways
Jealousy when a new sibling arrives is normal, nearly universal, and can last months. Regression in the older child – returning to earlier behaviours such as bedwetting, baby talk, or demanding a bottle – is one of the most common responses and reflects the child's attempt to reclaim an earlier, simpler state. How parents respond to the older child's feelings rather than their behaviour is the key variable. Research by Judy Dunn at the Institute of Psychiatry found that the quality of the mother-child relationship before the birth strongly predicts sibling relationship quality afterwards. Sibling relationship quality in childhood predicts adult sibling closeness and has benefits for both children's social development.
