why we say Micky mouses not Micky mice?
First of all, it's Mickey Mouse. When a common noun is also a proper noun, we don't use the same irregular plural rules for the proper noun that we use for the common.
Julia Child and her family would be the Childs, not the Children.
If you were looking in a shop window and there were lots of Mickey Mouse toys then you might say 'Look at those Mickey Mouses' because Mickey Mouse is a proper noun. The plural of mouse is mice, but not in this context.