Both child and kid refer to young people, but they differ in formality and usage.
  • Child is a formal noun for a young person, typically from birth to adolescence.
  • Kid is an informal synonym for child, used in casual conversation.
  • Child is preferred in legal, educational, and official contexts.
  • Kid is common in everyday speech and may appear in lighthearted contexts.
Child
'Child' is used in formal contexts such as legal, educational, and official settings.
'Kid' is commonly used in casual conversation and informal settings.
  • vs -
AspectChildKid
MeaningYoung person (birth to adolescence)Young person (same as child)
UsageFormal, officialInformal, casual
ContextsLegal, educational, officialEveryday speech, informal writing
ConnotationNeutral, seriousFriendly, casual
PluralChildrenKids
Summary:
Child is a formal term for a young person used in official contexts, while kid is its informal counterpart, common in everyday conversation.
'Kid' is the informal term for 'child'.
'Kid' can be used both as 'kid' (singular) and 'kids' (plural).
'Child' is more likely to be used in a school report.
'Kid' would not be appropriate in a job application.
The correct plural forms are 'children' for child and 'kids' for kid.
A lawyer would use 'child' in court.
'Kid' is suitable for informal speech to friends.
A textbook would likely use 'child'.
'Child' and 'kid' are not interchangeable in all contexts due to formality differences.

Sources

'Child' is formal; 'kid' is informal, per Merriam-Webster.
Authoritative definitions are in Merriam-Webster, OED, and Cambridge Dictionary.
  • https://www.merriam-webster.com/dictionary/child
  • https://www.merriam-webster.com/dictionary/kid
  • https://www.oed.com/
  • https://dictionary.cambridge.org/
Conclusion:
Child and kid both denote young people, but child is formal and used in official settings, while kid is informal and common in everyday speech.
  • Child is for formal, legal, educational, and official contexts.
  • Kid is casual and used mainly in spoken language or informal writing.
  • Choosing the right word depends on the situation's formality.