This is the 1349th most frequent Japanese word.
らしく
"らしく" means "seeming like" or "characteristic of."
Here, 'らしく' is used to describe behavior that is typical of the characteristic of 'child'.
彼女は子供らしく無邪気に遊んでいます。
She plays innocently like a child.
In this sentence, 'らしく' is utilized to indicate actions typical of the characteristic of 'adult' behavior.
彼は大人らしくしっかりと責任を果たしています。
He responsibly fulfills his obligations like an adult.
In this example, 'らしく' expresses a state that is characteristic of 'spring'.