There are many wonderful piano teachers around, but along with those, there are also many who play piano themselves, but shouldn’t be teachers. That might be because they can’t express themselves well and explain the concepts, or it sometimes might be that they really don’t know much themselves.
Before you get a piano teacher for you or your child, make sure that music theory is included in the lessons — learning all about note values, timing, intervals, chords, and so on. It’s excellent if the teacher uses workbooks so you or your child can methodically work through theory step by step.