幼稚的小孩用英语可以称作 "infant" 或 "toddler"。
"infant" 来源于拉丁语 "infans"，意思是不能说话的。
"toddler" 来源于中世纪英语 "todeler"，意思是蹒跚学步的小孩。
例句：
"She's taking care of her infant brother while her parents are away." (她在父母不在时照顾她的婴儿弟弟。)
"The toddler was just learning to walk, so he was always stumbpng around." (小孩正在学走路，所以总是蹒跚而行。)