Discussing with children (always at an appropriate age) that Holocaust denial is a big problem in the world, and why it's a big problem, would be fine with me. Catholic schools should be telling the kids about other religions and none (mine didn't, except to peddle the untruth that only Catholics went to heaven). Etcetera. But giving any kind of platform to Holocaust deniers, or to legitimise Holocaust denial by promoting those views as a respectable equal-but-opposite, is simply telling lies to children.