However, my mother sometimes behaved like a hen looking out for her little ones for fear one of us could slip away.

slip 的意思是"滑、溜"，常用来形容悄悄或不经意地移动。 away 是副词，表示"离开、远离"的意思。 slip away 这个短语表示"悄悄溜走"或"不知不觉地消失"，常用来形容不被察觉地离开某个地方或状态。