孩 puts the child radical 子 next to 亥 for sound. Its earliest meaning was a baby's laugh — the gurgle of an infant — before settling on the child itself. The giggle became the kid.
孩子 is the everyday word for child; 男孩 a boy, 女孩 a girl. Chinese parents call grown children 孩子 forever — a 40-year-old walking into their mother's home is still her 孩子, and will still be told to wear warmer clothes.
A child 子 whose first word is a laugh — the CHILD character.
熊孩子 'bear child' is internet slang for a little terror — the kid who deletes your save file and smashes your phone. Every family has one.