the baby tooth and permanent tooth? Has decay already started on the permanent teeth?

I get this a lot from parents. But decay progresses quickly in baby teeth, and when considering the teeth are much smaller than permanent teeth it can go from needing a filling to needing more (pulpotomy w/ stainless steel crown, extraction/space maintainer) very quickly. It can also spread from the primary teeth to the permanent teeth, especially if they are touching. Post some X-rays if you have them.