RESEARCH_FILE
Firstborn Adjustment Arc
The firstborn adjustment arc describes the predictable, time-limited trajectory of behavioral changes in firstborn children after a sibling's birth: an initial disruption phase (sleep disturbance, clinginess, regression, attention-seeking) that peaks in the first one to three months, followed by gradual normalization as the firstborn integrates the sibling into their social world. Dunn and Kendrick's longitudinal research shows this arc is nearly universal and does not reflect permanent damage — it reflects a normal stress-response to a changed family environment. Parental guilt typically outlasts the arc itself.
SEE THE PRACTICE
Turn a thought this research explains into one clear move.
THE THOUGHT
“My first child will feel replaced and never recover”
YOUR RECORDED RESPONSE
“Genuine disruption isn't the same as permanent wound. I can hold both at once.”
ONE PRIVATE MOVE
Write down one specific, repeatable thing you'll do with or for your first child that belongs only to that relationship, then read it once without editing. Do this before you scroll away.
How it sounds in your head
The inner script: 'My three-year-old has started wetting the bed again and demanding I carry her everywhere — I've broken her.' The research reframes the timeline: regression and clinginess in the weeks after a sibling's birth are among the most-documented, most-temporary phenomena in developmental psychology. The guilt the parent feels is often more durable than the child's disruption.