When do corrections need to be made with language learners? When does Erasmian pronunciation cross the line and need to be corrected?

When do corrections need to be made with language learners? When does Erasmian pronunciation cross the line and need to be corrected? Children need a stress-free environment for play and learning. Parents correct their children's speech, but not everything all at once and most of the time most any understandable utterance is accepted and praised. [...]