I have heard some Taiwan (and maybe Mainland) parents call their daughters měiméi. I'm wondering what is the reason for that.
The pronunciation of 妹妹 (mèimei) could have been mixed up with that of 美眉 (měiméi) due to the popularity of Taiwan TV dramas where the Taiwanese cast tend to pronounce 妹妹 similar to that of 美眉, for example, in shows such as 《星星知我心》.
美眉 (or MM in short) is a term used to describe young and pretty women. This term is to 妹妹 what 葛格 (gége) is to 哥哥 (gēge). The 美眉 article on Baidu explains this: