A phrase praising a child or person for good behavior; can also mean someone obedient, and sometimes used ironically.
「いい子にして待っててね」と母が子どもに言った。
Mother told the child, 'Behave yourself and wait, okay?'
病院で先生に褒められて、彼はいい子と呼ばれた。
He was praised by the doctor at the hospital and called a good boy.
うちの犬はとてもいい子で、散歩中もちゃんと戻ってくる。
Our dog is a very good boy and reliably comes back during walks.
いい子でいることが必ずしも簡単ではない。
Being a 'good child' is not always easy.