Hello @mariano_6259,
Thank you for your message. I am sorry you are having this problem.
I think the problem is that there is too much skin showing on the people in this image and that is flagging the image, unrelated to adding a moustache. Some people have handled this issue by taking the image into Photoshop and masked most of the image except the face of the baby, and the done a generative fill of a moutsache on the face. You can then remove the mask.
Thanks,
droopy