What is actually happening

Separation anxiety is not a behaviour problem and it is not something you caused. It is what happens when a baby's understanding of the world advances faster than their sense of time.

The step underneath it is object permanence: the discovery that things — and people — continue to exist when they cannot be seen. Before that, a parent leaving the room simply stopped existing, which is oddly untroubling. Afterwards, the American Academy of Pediatrics explains, a baby discovers "there's only one of you" and lacks the sense of time to anticipate your return. They know you still exist. They just do not know that you are coming back in twenty minutes, because twenty minutes means nothing yet.

The AAP is worth quoting on what this says about your relationship: "The predictable anxieties of this period are evidence of her healthy relationship with you." And: "If your child has a strong, healthy attachment to you, her separation anxiety probably will occur earlier than in other babies."

What is normal, as a range

The AAP's timeline: "some babies display object permanence and separation anxiety as early as 4 to 5 months of age", but "most develop more robust separation anxiety at around 9 months". It "usually peaks between ten and eighteen months and then fades during the last half of the second year". Some children take a different route entirely: "many toddlers skip separation anxiety in infancy and start demonstrating challenges at 15 or 18 months of age".

So the honest range runs from about four or five months at the earliest to well into the second year, with the crescendo somewhere between ten and eighteen months. There is no single correct month.

The CDC's nine-month milestone checklist puts the same thing in observable terms. Among the social and emotional milestones most babies show by nine months: "is shy, clingy, or fearful around strangers", "reacts when you leave (looks, reaches for you, or cries)", and "smiles or laughs when you play peek-a-boo". That last one is not filler — peek-a-boo is object permanence being rehearsed as a game.

Stranger wariness is part of the same step

The AAP describes a baby who can seem like two different children: open and affectionate with you, "anxious, clinging, and easily frightened around unfamiliar people or objects". The cause is not temperament but capability — your baby is "now, for the first time, able to tell the difference between familiar and unfamiliar situations".

It shows up at night too

The Sleep Foundation names "emotional development that can increase separation anxiety" among the drivers of the sleep disruption many families see around eight months, alongside teething and new physical skills like crawling and pulling to stand. If bedtime has suddenly become a battle at the same age as the clinginess, those are the same phenomenon, not two problems.

What actually helps

Say goodbye. Do not sneak out.

This is the single most repeated piece of advice and the most commonly ignored. The CDC's tip for nine-month-olds: "Say a quick and cheerful goodbye instead of sneaking away so your baby knows you are leaving, even if he cries. He will learn to calm himself and what to expect. Let him know when you return by saying 'Daddy's back!'"

Slipping away avoids one bout of crying and buys a baby who watches you constantly for the rest of the week.

Short, warm, and then actually gone

The AAP: "Don't make a fuss over your leaving. Instead, have the person staying with her create a distraction... Then say goodbye and slip away quickly." A prolonged goodbye extends the hardest part rather than softening it.

Time it well

The AAP suggests scheduling departures "after she's napped and eaten". A tired, hungry baby has fewer resources for anything, including you leaving.

Practise, in small doses

The AAP suggests using ordinary moments: when your baby crawls into another room, "wait for one or two minutes" before following, and "tell her where you're going and that you'll return". Before formal childcare starts, arrange playdates and visits, and "spend a few extra minutes playing with her in this new environment" on the first drop-offs.

Be predictable, and keep your word

The AAP's list includes quick goodbye rituals, using the same routine at the same time each day, giving full attention during the goodbye and then leaving, always returning when you said you would, and describing your return in terms a baby can use — "after nap time" rather than "at four o'clock".

What is not typical

Clinginess and protest at goodbyes are expected. What is worth a conversation is a child who cannot be comforted by a familiar carer at all after you have gone, a child who is distressed for hours rather than minutes every time, a child who was settling and has clearly gone backwards over weeks, or a loss of skills alongside the anxiety. The CDC asks families directly: "Has your baby lost any skills he/she once had?"

When to speak to a health visitor or doctor

The AAP's threshold is refreshingly low: "If you're concerned that your child isn't adapting to being without you, chat with the pediatrician." In the UK, the nine-to-twelve-month development review is designed for exactly this — the NHS says it looks at "language and learning, safety, diet and behaviour", and you will be sent an Ages and Stages Questionnaire (ASQ-3) to complete beforehand.

Contact your health visiting team between reviews if the distress is severe and unrelenting, if it is preventing your baby from eating or sleeping, if a childcare setting is telling you your baby cannot settle at all, or if it is affecting your own wellbeing. None of those require you to wait for the next appointment.

Separation Anxiety