I heard that small children get offended by hearing that their favorite teacher was wrong about something. But somehow this effect gets weaker as they grow up.

A part of it may be realising that humans make mistakes, even humans we love and respect. But I suspect another important part may be that as we grow up, the details of beliefs of elementary-school teachers are forgotten, and the high-school teachers don't have the same impact on us because we meet them older. At some moments people realize their own parents make mistakes, which starts with a big disappointment, and then gradually becomes just an acceptable fact about fellow humans.

Small children are quite helpless, and in a society more tolerant of harming or abandoning them (eg. the ancestral environment), offending the adults around them carried severe risks. Teenagers and adults could probably better afford to express disagreement.