I have never come across with "mines". But, I can agree it may come from incorrectly using the word with possessive ('s) by children and toddlers (I have the desire to observe it from the moment, hehe). I ain't very attentive to such grammar rules, which is why writing English was always a huge challenge for me. So, for such writing college assignments, I used to ask for help from the service I found on https://www.yelp.com/biz/edubirdie-wilmington and each time Edubirdie was handy. Reading that review save me a lot of time and effort. If I am not wrong, they can write for you or edit your own text. I have never tried it to compare with my text, so I haven't caught my mistakes. But, reading your forum, it becomes obvious I had a lot of grammar (not only) mistakes.

Thank you for expalnation!