Babies show the first signs of jealousy around 6 months of age. That’s earlier than many parents expect. In controlled experiments, 6-month-olds displayed clear negativity when their mothers gave attention to a lifelike baby doll compared to when their mothers interacted with a book. The reaction was specific to a social rival, not just any distraction, which is what makes it jealousy rather than general fussiness.
Why 6 Months Is the Turning Point
At around 6 months, babies have developed enough social awareness to track where a caregiver’s attention is going and to care when it’s directed at someone else. Before this age, infants can feel distress when a parent stops engaging with them, but they don’t yet seem to distinguish between a parent turning away to look at a book versus turning away to cuddle another baby. That distinction is the core ingredient of jealousy: it’s not just “you stopped paying attention to me,” it’s “you’re paying attention to someone else instead of me.”
By 9 to 13 months, jealous reactions become more intense and more obvious. Once babies can crawl or walk, they physically insert themselves between a parent and a rival. Researchers describe these as “assertive restorative bids for contact,” which in plain terms means the baby crawls over, reaches up, fusses, and does whatever it takes to reclaim the parent’s attention. Some of these bids include outright aggression.
What Jealousy Looks Like in Babies
Infant jealousy doesn’t look like adult jealousy. There’s no sulking or side-eye. Instead, it shows up as a cluster of behaviors that researchers have documented across multiple age groups:
- Sadness. This is the most consistent facial expression across studies, appearing in babies as young as 6 months and persisting into toddlerhood. It’s the same droopy, downturned expression you’d recognize in an older child.
- Approach behavior. Babies try to get closer to the parent. In younger, nonmobile infants (6 to 9 months), this looks like reaching, leaning, and maintaining gaze toward the parent. In mobile babies (10 to 13 months), it’s full-body movement toward the caregiver, often with urgency.
- Fussing, crying, and aggression. When softer bids for attention don’t work, babies escalate. They may cry, push at the rival (whether it’s a doll, another baby, or a sibling), or become physically disorganized in their distress.
- Gaze aversion. Some babies cope by looking away entirely. Researchers interpret this as a self-regulation strategy, the infant equivalent of “I can’t watch this.”
One study that measured brain activity found that only during the social rival condition (not when the parent attended to an object) did infants show a specific pattern of left frontal brain activation paired with negative emotions and approach behavior. In other words, the brain response to a social rival is measurably different from the response to a simple loss of attention.
What Triggers Jealousy
The most reliable trigger is a parent giving focused, warm attention to another person, especially another child. In experiments, researchers typically have a mother hold and talk to a realistic baby doll while ignoring her own infant. The babies respond with increased arousal, more aggression, more negative facial expressions, and more attempts to touch or get close to the mother. When the same mother ignores the baby to read a book, the reaction is significantly milder.
In everyday life, this translates to predictable scenarios: a parent holding a friend’s baby, a caregiver cooing over a newborn sibling, or even a parent giving sustained attention to another toddler at a playgroup. The key ingredient is that the attention is going to a social rival, someone who could theoretically replace the baby in the parent’s affections.
The Evolutionary Logic Behind It
Jealousy this early in life isn’t a flaw in development. It’s a survival mechanism. From an evolutionary perspective, a baby’s biggest competitor for parental resources (food, protection, warmth, attention) is a sibling. The fact that jealousy-driven protests and separation anxiety both emerge around 9 months is likely not a coincidence. That’s roughly the age when, in ancestral environments, a new sibling’s birth became possible.
The goal of jealous behavior isn’t just to be near a caregiver. It’s to have exclusive access to that caregiver. Researchers describe this as the difference between seeking proximity and seeking exclusive proximity. A baby who successfully reclaims a parent’s full attention has, in evolutionary terms, secured continued access to the resources they need to survive.
How Jealousy Changes With Age
At 6 months, jealousy is primarily emotional. Babies feel it, their faces show it, but their limited mobility means they can’t do much about it beyond fussing and reaching. Between 10 and 13 months, the physical component ramps up dramatically as babies gain the ability to crawl and walk toward the parent, push at rivals, and make loud protests.
By the toddler years (around 18 to 24 months), jealousy begins to blend with more complex emotions and behaviors. Toddlers can be verbally possessive (“my mommy”), deliberately disruptive, or regressive, returning to behaviors like thumb-sucking or wanting a bottle they’d already outgrown. When a new sibling arrives, common reactions include aggression toward the newborn, attention-seeking behavior, and regression, but also, sometimes, surprising bursts of independence and maturity. Children often swing between these extremes as they adjust.
Helping Your Baby Through Jealous Feelings
You can’t prevent jealousy, and you shouldn’t try. It’s a normal, healthy part of emotional development. What you can do is manage the environment so your baby feels secure.
If you’re introducing a new sibling, stay physically close whenever both children are together. If you see the older child getting rough, pick up the baby and redirect the older child with a toy, a snack, or a song. This protects the newborn without turning every interaction into a string of “no,” which can actually encourage the aggressive behavior you’re trying to stop. Teach the older child gentle ways to be physical with the baby, like giving a back rub, and praise them when they do it well. This channels the impulse to touch the baby into something positive.
Watch how you talk about the baby in front of the older sibling. Constantly saying “we can’t go because of the baby” or “be quiet, the baby is sleeping” turns the newborn into the reason for every frustration. Use neutral alternatives instead: “we’ll go after lunch” or “my hands are busy right now.”
Name your child’s feelings without dramatizing them. “Things sure have changed around here” or “it must be hard to wait when I’m busy with the baby” lets your child know you see what they’re going through. When children feel understood, they have less need to act out to get your attention. And increase the small demonstrations of love: extra hugs, extra “I love yous,” a few minutes of undivided attention with a book or a game. In a time of adjustment, those moments matter more than you might think.