Young children are not born with fully developed emotional control or stress-management skills. These abilities develop gradually during early childhood through repeated interactions with caregivers and the environment around them. Early childhood is considered a critical period for the development of biological and behavioral regulation systems(1,2).
In the earliest years, parents often function as external support systems for regulation. Over time, children are expected to take on more of this work themselves. This study asked an important question, which is how does that transition normally unfold, and what happens when parenting becomes harsh or stressful?
Researchers focused on a physiological measure called respiratory sinus arrhythmia (RSA). RSA reflects how the body’s parasympathetic nervous system, the part of the nervous system involved in calming and recovery, responds during stress and social interactions. In simple terms, RSA provides a window into how flexibly the body can adjust when demands change. RSA is widely used as a marker of self-regulation and adaptive responding during social and emotional challenges(3,4).
You can think of RSA as a measure of the nervous system’s ability to shift gears efficiently.
A well-regulated system can:
A less flexible system may:
To study this, researchers measured RSA in mothers and preschool-aged children while they worked through difficult puzzle tasks together when children were ages 3 and 4.
Self-regulation refers to the ability to manage emotions, attention, behavior, and physiological responses in ways that fit the situation.
Preschool years are particularly important because these skills are developing rapidly during this period(1).
Coregulation refers to the process by which caregivers help children manage emotions and stress before children can consistently do it themselves. Young children are not expected to regulate independently.
Over time, children gradually internalize these experiences and begin regulating more independently. Theories of parent-child development suggest that this shift from caregiver-driven regulation toward greater child independence is a normal part of development(2,5).
At age 3, mothers strongly influenced their children’s physiological responses during challenging tasks.
Researchers found that mothers’ and children’s nervous systems were linked in real time. Changes in mothers’ physiological state were followed by changes in children’s stress responses.
This pattern supports the idea that young children initially rely heavily on caregivers to help organize their emotional and physiological responses to difficult situations(2).
Between ages 3 and 4, children generally became less dependent on maternal regulation.
This pattern suggests that children were beginning to internalize regulatory skills and rely more on their own developing capacities.
More child independence. Less parent-driven regulation.
Researchers viewed this as evidence that regulation normally becomes more self-directed as children mature(5).
One of the study’s most important findings involved the effects of harsh parenting.
Rather than gradually shifting toward independence, these children appeared to remain more reliant on external regulation. Prior work suggests that harsh parenting and maltreatment can disrupt physiological regulation and increase risk for later emotional and behavioral difficulties(6,7).
The reason this matters is rooted in how children’s stress systems develop.
Children expect caregivers to function as reliable sources of safety. When caregiving becomes unpredictable, threatening, or emotionally harsh, the nervous system may adapt in ways that prioritize vigilance and stress responsiveness rather than flexibility(2,6).
One of the more technical concepts in the study was RSA inertia. RSA inertia refers to how strongly the body stays in its current physiological state from one moment to the next. A useful way to think about it is recovery speed after stress.
Stress response activates → challenge passes → body recovers efficiently
Stress response activates → body remains activated longer than needed
Children exposed to harsher parenting showed increasing RSA inertia over time.
This suggests that their physiological stress systems became less flexible and slower to recover, which could make adapting to challenges more difficult. Research increasingly suggests that physiological flexibility may be important for healthy emotional development(3,8).
Early childhood is a period when the brain and nervous system are especially adaptable.
These experiences are not only shaping behavior. They are helping build the biological systems that support emotional regulation throughout life(1,2).
Young children rely heavily on caregivers to help regulate stress and emotions in the early years. As development progresses, that support usually becomes less necessary as children build stronger self-regulation skills.
This study suggests that harsh parenting may interfere with that transition. Children exposed to harsher caregiving showed increasing difficulty regulating stress and remained more dependent on external regulation over time.
The findings reinforce an important idea, which is caregiving does not simply shape behavior. It helps shape how developing stress systems are built.
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