From Parents and Children, Chapter V:
‘I don’t know’ must take the place of the vague wise-sounding answer, the random shot which children’s pertinacious questionings too often provoke. And ‘I don’t know’ should be followed by the effort to know, the research necessary to find out. Even then, the possibility of error in a ‘printed book’ must occasionally be faced. The results of this kind of training in the way of mental balance and repose are invaluable.