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Fussy behaviour in babies - wonder weeks

fussy; fussing; regression; weeks; unsettled; crying; development; infant; baby; behaviour; wonder; cling; sunny; growth; spurts;

Some people who have researched baby development and behaviour think that there may be predictable times during the first year of a baby's life when a baby may be more demanding (fussier) than usual, and other times when a baby may be calmer. The fussy times have been called the 'wonder weeks' by some writers (see below), because it is during these more difficult weeks that babies are making big steps forward in their development.


These changes in the way your baby is behaving week by week may occur in cycles over the first year or so. In some babies these patterns of changing behaviour may be clear, while for others they may not occur, or they may not be clear.  There has been some research that suggests these cycles of changes in behaviour may happen in many different cultures.

Other things can cause differences in behaviour day by day and the way that a baby manages changes in his or her life, such becoming anxious such as when separated from his mother (separation anxiety), changes in what is going on around him, and minor illnesses or pain such as nappy rash or sore ears. Teething has been claimed by many people to affect behaviour, while some research has shown that it probably is not the cause of a baby being fussier than usual.

A baby’s temperament - whether they tend to be calm and easy to get on, or find changes and life in general more difficult – can lead them to be more or less fussy that other babies much of the time. Calm babies tend to be happier, cry less and go to sleep more easily.  But even calm babies may have days when they seem more easily upset than other times for no reason that can be worked out.

Fussy weeks - 'wonder' weeks

We know that development in physical skills happens in 'steps' - one day a baby can take a step and start to walk, whereas the day before he could not take that step. Similarly, it is thought that the way that a baby can think, feel, notice and understand what is happening around him (mental development) might also happen in steps.

  • For example, at around the age of 8 weeks, a baby can begin to recognise more of the people and things that she can see around her.
  • At about 6 months she can start to realise that some people are around most of the time (her parents for example), while some people are strangers. Before that time she did not know that some people were strangers.

There is much more about this in our topics on child development in the Growth and development section of this website,

Changes in thinking can show up in changes in what a baby can do, and how she behaves. During these times when a baby's ability to understand the world around them is changing, she may need more attention.  

  • She may cry more, be more fussy and need more comforting. This may be due to other reasons, such as being unwell.
  • Some of the babies lose their appetites.
  • Some babies who have been sleeping well may take more time to go off to sleep and wake more often.
  • Some young children who have been happily exploring their world may become more clingy, and become upset much more easily.
  • They may show an increased need for body contact with their mothers or other caregivers. 

Sometimes babies or young children will seem to have gone backwards in their development. In fact, they are making a big step forward, but this step is confusing to them, and they may behave more like a younger baby.

Calmer 'sunny' weeks

When babies have fully 'climbed' this developmental step, there may be several weeks when they are happier. They can happily try out their new skills. They may be less easily upset. They may allow you to be out of sight more often, and go off to sleep more easily.

Other things that can cause a baby to be fussy

Babies can be fussy for many other reasons.

  • A baby who is unwell or in pain is likely to be more distressed than usual. A nappy rash, for example, is very painful, and will cause a baby to cry more and have more difficulty going to sleep and have restless sleep.
  • It is often thought that babies are unsettled when they are teething. Research has suggested that babies are not more distressed when they are teething, but not everyone is convinced. Maybe the teething has coincided with a fussy developmental stage.
  • An older baby who is separated from their parents may be very distressed when they return. This is likely to be due to separation anxiety, not 'just a phase'.
  • Some babies have developmental delays or major health problems, which could alter the times that they go through these mental developmental milestones.

How to help your baby during fussy weeks

  • During fussy weeks, babies seem to manage the developmental changes more easily if they get extra attention, get held more often and have extra comforting when they go to sleep. They need this extra attention: it is not just because they are choosing to be more demanding.
  • It may help to know that despite the difficult times, there will also be times when your baby will be happier and more easy to get along with.
  • If parents are not able to give babies as much attention as they need, their baby may find this mental developmental step more difficult to manage.

Is it possible to predict the fussy (wonder) weeks?

It is claimed that many babies follow a similar pattern, and so it may be possible to predict approximately when a child may have a fussy ('stormy') time. The times listed below are approximate times -  they can vary for baby to baby, and babies may pass through these times wihout seeming to be fussier than usual.

In the first year of life, the stormy times seem to happen around

  • 5 weeks
  • 8 weeks
  • 12 weeks
  • 17 weeks
  • 26 weeks (6 months)
  • 36 weeks
  • 44 weeks
  • 53 weeks (around 12 months).

Even though the fussy weeks can seem like difficult times when babies are clingy and unhappy, they are very special weeks because babies are making a new big step forward.

There is more information about each 'wonder week' - about what development stage may be happening during a 'wonder week' in the book by Vanderrijt, H. & Plooij, F. (2013)
The Wonder Weeks.   

Just as physical developmental stages do not stop when a child reaches 12 months of age, mental developmental stages will also continue, and there will continue to be 'good' weeks and more difficult weeks. Any parent of a teenager will be able to confirm that they still are having good and bad weeks.

Predicting 'sunny' weeks

The 'sunny' weeks may also be more or less predictable. The 'sunniest' weeks may happen around

  • 6 weeks
  • 10 weeks
  • 13 weeks (around 3 months)
  • 21 weeks
  • 31 weeks
  • 39 weeks
  • 49 weeks
  • 58 weeks.


Even though 'wonder' weeks can seem like difficult times when babies are clingy and unhappy, they are very special weeks because babies are making a new big step forward.


For more about Wonder weeks, including ideas about what may be causing these changes in behaviour: Frans X. Plooij (Author) van de Rijt Hetty ‘The Wonder Weeks: How to Stimulate Your Baby's Mental Development and Help Him Turn His 10 Predictable, Great, Fussy Phases into Magical Leaps Forward’ Paperback (2013) The Wonder Weeks 

Additional references

Richter, J. & Woolmore, A. (2004).  Regressive Periods, Maternal Depression and the Development of Insecure Attachment.  Paper presented to WAIMH World Congress, Melbourne, Australia. Jan .

Sadurni, M. &  Rostan. C. (2002) Regression Periods in Infancy: A Case Study from Catalonia. The Spanish Journal of Psychology. Vol 5, No. 1, 36-44.

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The information on this site should not be used as an alternative to professional care. If you have a particular problem, see a doctor, or ring the Parent Helpline on 1300 364 100 (local call cost from anywhere in South Australia).

This topic may use 'he' and 'she' in turn - please change to suit your child's sex.

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