When I was living in Korea for a few years, one of my responsibilities was teaching new workers some Korean. As to not upset clients (adults mainly) by speaking to them too informally, we always taught new workers to use 하십시오체 or 해요체. Moreover, they were instructed that 반말 was never to be used.
However, I occasionally saw some of my colleagues talking to children in 해요체, or even worse, 하십시오체. This always felt awkward, but I never quite knew if it was actually weird to talk to kids in 해요체 instead of 반말, or if it just felt weird to me personally.
Is it okay to talk to children in 해요체, or should it be avoided?