在那儿孩子们有个玩耍的花园.
正:There the children had a garden in which to play.(很正式)
正:There the children had a garden in which they could play.(较正式)
正:There the children had a garden to play in.(较口语化)
注:这类“介词+关系代词+不定式”结构中的介词不能没有,也不能放在句末.如不能说There the children had a garden which to play in.