mama's boy; mama's girl; mother's child
Colloquial, often slightly teasing term for a child who is overly attached to their mother. Can be used for boys or girls.
That kid is still a mama's child, always hiding behind their mother.
When my little brother was small, he was a real mama's boy.
Compound of ママ (mama) + っ子 (kko), a colloquial suffix meaning 'child' or 'person with a strong attachment'. The exact derivation is uncertain, but it follows a common pattern for such terms.