Cognitive Connie
Understanding cognitive development in toddlerhood
Toddlerhood (roughly 12 to 36 months) marks one of the most dramatic cognitive transitions in human development: the shift from sensorimotor intelligence to symbolic representation. Around 18 months, the child becomes capable of forming stable mental representations of absent objects and events — they can think about things that are not currently present. This representational capacity is the cognitive engine behind several signature achievements of toddlerhood: the rapid expansion of language, the onset of pretend play, and the emergence of deferred imitation.
Key figures
Jean Piaget
1896–1980Characterised the transition from sensorimotor to symbolic thought as a qualitative leap; his observations of pretend play and deferred imitation in toddlers remain foundational.
Lev Vygotsky
1896–1934Theorised the convergence of language and thought around age 2 as a pivotal moment in cognitive development, transforming thought into verbal reasoning and play into a leading activity of development.
Adele Diamond
1949–Neuroscience of executive function development; connected the A-not-B error to prefrontal cortex maturation and showed that inhibitory control underlies many apparent "cognitive" failures in toddlerhood.
Key concepts
Symbolic function (Piaget)
The capacity to use one thing to represent another — a word, image, gesture, or object standing for an absent referent. Emerges around 18–24 months at the end of the sensorimotor period. Underlies language, pretend play, deferred imitation, and mental imagery. For Piaget, symbolic function is the defining achievement that marks the transition from sensorimotor to preoperational thought.
Pretend play
The use of objects, actions, or roles in non-literal, "as if" ways — feeding a stuffed animal, using a block as a car. Emerges around 12–18 months, initially with self-directed actions, then extended to others and to substitute objects. Tracks broader symbolic development and is considered a reliable index of representational capacity in toddlerhood.
Language and thought (Vygotsky)
Vygotsky argued that language and thinking have separate developmental origins (the pre-linguistic stage of thought; the pre-intellectual stage of language) but merge around age 2, transforming both. From this point, thought becomes verbal and language becomes rational — a qualitative leap that enables increasingly sophisticated self-regulation and problem-solving.
Inhibitory control
The ability to suppress a dominant or prepotent response in favour of a goal-appropriate one. In toddlerhood, measured via A-not-B tasks and the Detour Reaching task. Extremely limited at 12 months, it develops substantially across toddlerhood and early childhood, driven by prefrontal cortex maturation. Foundational to later executive function, emotion regulation, and academic readiness.
Working memory (early development)
The capacity to hold and manipulate information in mind over short periods. In toddlerhood, working memory is extremely limited — typically one to two units — but expands substantially across the preschool years. Underlies object tracking, simple problem-solving, and early language comprehension. Prefrontal and parietal development drives its expansion.
Causal understanding
Toddlers develop an understanding that events have causes, distinct from mere association. By 24 months, toddlers show a preference for causal over coincidental sequences; they can use a tool to retrieve an out-of-reach object (demonstrating means-ends reasoning), and they infer hidden causes from incomplete evidence. This emerging causal framework is foundational for later scientific reasoning.
Test your knowledge
Sources
Last reviewed August 2025- 1.
Vygotsky, L. S. (1978). Mind in Society. Harvard University Press.
+About this source
Foundational text on the relationship between language and thought, the ZPD, and the role of play in cognitive development.
- 2.
Diamond, A. (2002). Normal development of prefrontal cortex from birth to young adulthood. In D. T. Stuss & R. T. Knight (Eds.), Principles of Frontal Lobe Function (pp. 466–503). Oxford University Press.
+About this source
Comprehensive review of prefrontal cortex development and its relation to executive function from infancy through young adulthood.