[ummwhat]

This assumes a normative value of truth being good. You could be ambivalent on the truthfulness of adults, accepting early on that everyone lies some fraction of the time and it's ok for you to do it too. The badness of lying is a societal rather than universal value. Kids lie all the time when they think it will work, so why would they be surprised or offended when it happens?

The real hat trick is to lie to the adults about still believing in Santa so the presents keep on coming. A con so deep the marks think they're the ones pulling the con.