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On the move: baby separation anxiety and crawling (weeks 26 to 39)

Window 4 of the Fussy Phase Forecast · Last verified: July 7, 2026

The short answer: your baby is working on two huge projects at once: moving their body and figuring out who their people are. The clinginess and stranger-shyness that show up in this window are not steps backward. They are official 9-month milestones, and a sign your bond is working exactly as designed.

The clinginess plot twist

Here is the reframe that saves this whole window. Around now, many babies who were happy to be passed around suddenly protest when you leave the room, and eye strangers with deep suspicion. It feels like regression. It is the opposite.

“Is shy, clingy, or fearful around strangers” and “reacts when you leave” are on the CDC’s official list of what most babies do by 9 months (CDC milestone checklist). Your baby has figured out two big things: you are their person, and people exist even when they cannot see them. The crying at the door is that new knowledge, out loud.

The NHS says it plainly: separation anxiety is common from around 6 months to 3 years, it is a normal part of development, and it is usually a sign of how well you have bonded (NHS: Separation anxiety). Leaving your baby with another trusted caregiver does not damage them. It teaches them the most reassuring lesson there is: you leave, and you come back.

What helps, per the NHS:

• Practise short separations first (a few minutes, with someone your baby knows well), then build up
• Leave something that smells or feels like you, or a favourite toy
• Say goodbye with a smile and confidence, even if your heart is breaking a little; babies read your tension
• Have happy, warm reunions, so the pattern “leaves, then comes back, and it’s good” sinks in

And a threshold worth knowing: if your child is very distressed, stays upset for a long time after you leave, or it goes on for more than a few weeks, the NHS suggests talking to your health professional. That is a conversation, not an alarm.

The rough patches around weeks 26, 30 and 36

The 1992 week-by-week study described three fussy clusters in this window, around weeks 26, 30 and 36 (the research, reviewed here). Three sounds like a lot, and this stretch can genuinely feel bumpy: big motor work, big feelings about you, sometimes new teeth, all at once.

Same honesty as always: the exact weeks did not hold up when other researchers checked, and babies vary hugely. Use these numbers as a “this stretch can be bumpy” heads-up, not as three appointments with misery.

Bodies in motion (and a note about crawling)

By 9 months, most babies get to a sitting position by themselves and sit without support. They move things from hand to hand and rake food toward themselves with their fingers (CDC).

Notice what is not on that list: crawling. The CDC’s 9-month checklist does not include it at all. Babies get around in wildly different ways at this age, on different schedules, and the official checklist simply does not treat crawling as a required stop on the route. So if your neighbor’s baby crawls laps while yours perfects the art of sitting, the checklist is on your side.

Whatever the method, movement is coming. Now is the moment to look at your floors the way your baby soon will: everything within reach, everything a possibility, everything headed for the mouth.

What most babies do by 9 months

The full CDC list, based on what at least 75 percent of babies actually do (CDC, scientific basis in Zubler et al., Pediatrics 2022):

• Is shy, clingy, or fearful around strangers
• Shows several facial expressions, like happy, sad, angry, and surprised
• Looks when you call their name
• Reacts when you leave (looks, reaches for you, or cries)
• Smiles or laughs when you play peek-a-boo
• Makes different sounds like “mamamama” and “babababa”
• Lifts arms up to be picked up
• Looks for objects when dropped out of sight, like a spoon or toy
• Bangs two things together
• Gets to a sitting position by themselves, and sits without support
• Moves things from one hand to the other
• Rakes food toward themselves with their fingers

Born early? Count from the due date. The adjusted age is what development follows, and it is what our forecast uses.

The 9-month check-up matters a little extra

One practical thing to know: 9 months is when the American Academy of Pediatrics recommends a general developmental screening for all babies, not just ones with concerns. It is a standard part of the well-child visit. If it does not come up, ask about it (noted on the CDC’s own 9-month checklist).

When to call your pediatrician

The CDC’s rule: if your baby is missing one or more of these milestones by 9 months, or has lost skills they once had, do not wait and see. Talk with the doctor and ask about developmental screening.

And as always: your own concern is reason enough to call.

Keep reading

• Previous window: Weeks 17 to 26: grabbing everything
• Next window: Weeks 39 to 52: almost a toddler
• Adjusted age for premature babies

Sources

• CDC: Milestone checklists, 2022 revision
• Zubler et al., “Evidence-informed milestones for developmental surveillance tools”, Pediatrics 2022
• NHS: Separation anxiety
• van de Rijt-Plooij & Plooij (1992) and follow-up research, KNAW review

Peanutbean provides general information for educational purposes only. It is not medical advice. Every baby develops at their own pace. Always talk to your pediatrician about your child’s health.