He' s very good with children,ie can look after them well,amuse them,etc.
他很会照看孩子.
She was very intelligent and good with the girls.
它很有灵性,跟两个女孩子关系融洽.
I am not good at sports,but I like to watch them."
我不擅于运动,但我喜欢看.
He is good at farm work,though very young.
他虽然很年轻,却善于做农活.
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所以good with 多数用于说人的照顾,关系好,good at 用于说善于做什么.