We used Santa (et al.) as an exercise in critical thinking. Outside of saying, “Yep, the Easter Bunny did it.” we never directly lied about it. If they asked a question about it, we answered truthfully.
Child: “Whoa, how does he visit all those homes in one night?”
Dad: “It’s impossible unless he uses magic.”
C: “Whoa magic is real??”
D: “Nope.”
They all figured it out on their own before they hit grade school.