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"That's Not Fair": What Children Mean When They Say It, and How Jealousy Develops

By Leon MoriguchiPublished May 13, 2026Updated May 18, 20266 min read日本語版あり
Audience
Parents of children ages 2–6

TL;DR

  • ·Jealousy and envy are structurally distinct emotions — jealousy is a three-party fear of losing something held, envy is a two-party dissatisfaction over what another has — and a child's "that's not fair" may be carrying both at once
  • ·Proto-jealous responses are observable at six months before any language for the emotion exists; reliable vocabulary for "jealous" or "envious" does not appear until age four or later, meaning children feel these emotions long before they can name them
  • ·The full equality preference — objecting to unequal distributions regardless of who benefits — develops between ages 7 and 8; a four-year-old's "not fair" reflects a mix of personal envy and early, partial fairness reasoning, not a fully formed moral complaint

Contents

  1. Lead
  2. Jealousy and envy have different structures
  3. Jealousy is present at six months
  4. The gap between feeling and naming
  5. The development of fairness — "why does equal matter?"
  6. What parents can do
  7. Summary
  8. References

Lead

Most parents remember the first time their child said "that's not fair." It might have been directed at a younger sibling getting a parent's attention, or at a friend who had a toy the child didn't. The phrase carries a weight that surprises — it sounds both deeply felt and somehow adult.

Is it an emotional expression, a moral complaint, or both? The psychology of jealousy and envy — how these two distinct emotions develop in children, and how children eventually find words for them — offers a more specific answer than we might expect, and it changes how the phrase "that's not fair" sounds to a parent who hears it.

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