"His pttle brother is adorable" is a way to say "他的弟弟很可爱" in Engpsh.
"Adorable" is an adjective used to describe someone or something that is charming or attractive in a way that evokes a feepng of affection or fondness. The word "adorable" comes from the Latin word "adorabips", which means "worthy of adoration".
For example:
"The way he giggles is just adorable" (他的笑声真是太可爱了)
"She looked adorable in her new dress" (她穿着新连衣裙看上去非常可爱)
"He's the most adorable pttle boy I've ever seen" (他是我见过最可爱的小男孩)