adverb, adverb taking the 'to' particle
loudly; wailing; making a racket
Mimetic adverb describing loud, unrestrained crying, shouting, or noisy commotion, often by children or in chaotic situations. Can be used with と or as a standalone adverb.
赤ちゃんがわあわあ泣いている。
The baby is crying loudly.
子供たちがわあわあ騒いでいた。
The children were making a racket.
Reduplicated mimetic word from the sound of loud crying or noise. The exact origin is uncertain, but it imitates the sound of wailing.