They scream the second I leave the room

It arrives exactly when they can leave you

The timing is the explanation. Separation anxiety and wariness of strangers show up in the same months a baby starts to crawl, cruise and then walk — and Raising Children Network puts the reason plainly: babies are starting to move around more at this stage, and a baby who could crawl away from their carers without any fear of separation or strangers would get lost far more easily.

So the fear is not a malfunction. It is the safety feature that arrives alongside the mobility, and it arrives slightly ahead of it, which is why it can seem to come from nowhere in a baby who is not yet going anywhere.

AAP frames the cognitive half the same way: this is the first time your baby can tell the difference between familiar and unfamiliar, and the first time they have worked out that there is only one of you. They also have no sense of time, so when you leave the room they do not know when — or whether — you are coming back. From inside that head, the reaction is proportionate.

The age range, honestly

The two best sources give slightly different numbers, and the range is more useful than either alone. AAP describes stranger anxiety as one of the first emotional milestones, with separation anxiety peaking between ten and eighteen months and fading during the second half of the second year. Raising Children Network puts the start at 6-7 months and the peak at 14-18 months, easing gradually through early childhood.

Taken together: somewhere in the second half of the first year it starts, somewhere between ten and eighteen months it is at its loudest, and it thins out across the second year. A baby who starts at five months and one who starts at ten months are both inside normal.

It also varies enormously between children, and that variation is not a report card on anything you have done. Some babies are briefly unsettled; others are inconsolable at the sight of a coat being picked up.

One reliable amplifier worth knowing: AAP notes a baby is more susceptible when tired, hungry or unwell. The 5pm version of this is not the same child as the 10am version.

Say goodbye. Always say goodbye.

The strongest temptation is to slip out while they are distracted, because it avoids the scene. It is the one thing both sources tell you not to do. Raising Children Network is explicit that leaving without saying goodbye can make things worse — the child is confused and upset when they realize you are gone, and harder to settle the next time you leave.

The scene is the cost of a child who learns that departures are announced and survivable. Avoiding the scene teaches that you can vanish at any moment, which is a much worse thing to believe about the person you depend on.

So: settle them into something they are enjoying, tell them you are going and that you will be back, say goodbye briefly, and go. Do not extend it — a long goodbye is its own kind of alarm signal.

And keep your face relaxed while you do it. Raising Children Network makes this point specifically: if you look worried or sad on the way out, a child reads that as evidence the place is not safe, and gets more upset, not less.

Practice, rather than avoidance

The instinct is to minimise separations until it passes. Both sources point the other way: it is better not to avoid separation, but to build it in small, survivable doses.

Start short and lengthen. Leave the room announcing that you are going and coming back, and then come back — repeatedly, undramatically, at a distance and duration they can tolerate. What you are teaching is not toughness; it is that your leaving reliably ends.

For somewhere new — childcare, a relative's house — spend time there together before the first separation, and let them bring something of their own. A familiar object in an unfamiliar place does real work, and it can be phased out once the place stops being unfamiliar.

This is also, in Harvard's terms, serve-and-return doing its job: the return is what builds the expectation. A child who has been left a hundred times and collected a hundred times has evidence. That is the whole mechanism.

When it is worth raising

Separation anxiety that is severe, long-lasting and getting in the way of ordinary daily life is worth professional advice rather than patience — that is Raising Children Network's own threshold, and it is a sensible one.

In practice: still escalating well past the second birthday, distress that does not settle within a reasonable stretch after you have gone, or a child who cannot do the ordinary things of their age because of it.

The point is not that the fear itself is abnormal. It is that when a normal developmental phase stops thinning out on schedule, that is information worth having someone look at.