Parents should always have something up their sleeve to deal with challenges.

have 是动词，意思是"拥有、持有"。 up 在这里是介词，表示"在...上方"或"在...内部"。 sleeve 是名词，指"袖子"。 have something up one's sleeve 是一个习语，字面意思是"袖子里藏着东西"，引申为"有备用方案"或"有秘密武器"。