Child/tʃaɪld/ Definition 1 of 5Pro Tip 1/2Age-related Usage Use 'child' to describe someone typically under 18, but cultural views on age may vary. In my country, you're considered a child until you turn 18. Pro Tip 2/2Not Always Biologic 'Child' can refer to adopted individuals, not just biological offspring. They welcomed her as their child with open arms.