How can I treat melasma, especially on a young child? (age 12)

I've been noticing a dark patch on my daughter's upper lip which has been bothering her for more than one year. She tried shaving the area to see if it was just hair but it was still dark. She has been teased about it for a while now and I just discovered it's uncurable. Any home remedies or cheap creams that are helpful but safe for my child to use? I can't afford to pay for a dermatologist but I wish I could. Thank you to whoever answered this!