It Takes Two (1995)

Amanda Lemmon is a street-wise orphan who's about to be adopted by a family who uses children for their own selfish gain. Her case worker, Diane, loves her and would like to adopt her, however, since she's single and doesn't have money, she is unable to do so. Alyssa Callaway is a rich girl home from boarding school for the summer and she and her dad, Roger, go to their summer home. There, he tells her that he is marrying Clarice, a child hating gold digger. During an attempt to run away, Alyssa stumbles upon a summer camp where she runs into Amanda, who looks EXACTLY like her. The two then switch places to get rid of Clarice and unite Roger and Diane.