There are two stories; in the first Bats does everything he can to terrify the kid (who is orginally much less afraid of him than the other members of the gang), and the second is when Batman comes back to ask for Plas' help against The Burning, where Luke doesn't seem frightened in the slightest, after the original mention that he's kept out of that stuff. In both cases it came across as though a child is much less likely to be scared of Batman unless Bats puts special effort into it.