偶尔:
occasionally
e.g. There's no harm in your staying up late occasionally.
偶尔晚睡并无妨害。
sometimes
e.g. I differed with my partner sometimes, but we usually agree.
我有时与我的伙伴争论,但我们通常是一致的。
once in a while
e.g. He comes to our room for a chat every once in a while.
他偶尔来我们房中闲谈。
on some occasions
e.g. Therefore they kept the children on some occasions giving the "seller" a gift in return.
因此,有些时候,他们就会给这些“出售者”礼物作为回报,留下孩子们。