My son started kindergarten yesterday at our Catholic school and we took a bunch of pictures (yes, first child). One of them was a picture of him kissing a statue of the Blessed Virgin. Nobody told him to do it, he just did it. I think he picked up the idea from Good Friday, when everyone kissed the feet of the crucifix. He has kissed a statue of Mary or of Jesus a few times since Good Friday. Anyway, the picture was shared with family and friends, many of whom have raised eyebrows about it. Is it wrong for him to do that? Is it wrong for us to not stop him? What should we tell him about statues?
It sounds to me that you have no need to tell your son anything about statues right now. He already appears to have a very good idea of what they are for: To allow Christians to demonstrate their affection for God, his Mother, and his friends in a physical manner. As for your family and friends, all you need tell them is that your son was showing affection for his heavenly Mother, in a manner similar to how he might show his affection for them by kissing pictures of them in your family photo album.