also: よいこ
expression, noun
good boy; good girl
Used to praise a child for behaving well, or to describe a well-behaved child. Often used by parents, teachers, or in children's contexts.
今日はいい子にしていたね。
You were a good boy/girl today, weren't you?
いい子で待っていてね。
Be a good kid and wait here, okay?
いい is the more casual equivalent of 良い, used attributively. いい子 is a fixed expression meaning 'good child', while 良い is a general adjective meaning 'good'.
Compound of いい (good) and 子 (child). The reading いい is a colloquial variant of よい.