This parent is wrong, and the teacher is also wrong. There is no reason for children to use a source like Wikipedia for anything. Children also should not be permitted to use services like Google, which is bad for similar reasons, amply recited by the link author. Schools usually have access to excellent library databases. It's never too early to teach children useful research skills. Wikipedia is anti-useful. Search…
Exactly. To oversimplify, the correct advice has two parts: 1) don't use Wikipedia, 2) use these better sources instead. The teacher is wrong because they're apparently forgetting the second part, but the parent is also wrong because missing that doesn't make Wikipedia a good source.
IMHO, a pretty good lesson for schoolchildren is: quality information usually takes some effort to access, and information that's easily accessible is probably bad. That's because quality is usually expensive, so free very often takes shortcuts on quality or injects an agenda.