The white coating on the tongue sounds like thrush, which is yeast. To get rid of thrush, take 4 bayleaves in 2 cups water, simmer for 20 minutes. Let cool down and place several drops of the water on tongue several times per day. That should go away in about a day or so.
Was the child recently on antibiotics?
There are several ways to treat internal yeast. But first you must eliminate ALL sources of diary. Begin vitamin C. Get some Grapefruit seed Extract (GSE).. Follow the instructions on the bottle. Or you can go to the docs and DEMAND Nystatin. Try to avoid diflucan, it kills the yeast way too fast and causes horrible side effects. Agression, really bad smelly poops. Yeast dying is toxic.
I hope this helps. let us know.