^Honesty = Authority. How many children have had years worth of guilt and nightmares because they were told their dog or cat ran away or disappeared? "It's my fault that she ran away! I closed the door on her when she just wanted a pet." "I forgot to feed her" "If only I did this, she wouldn't have run off" – these kinds of thoughts circle around children's minds and torture them for years, all because a parent or aunt or uncle or grandparents thought they were "sparing the child's feelings" by not speaking the truth. Yes, your kids will think you as a horrible person for killing or throwing out their beloved pet without their permission, but they'll believe when you have other important news to tell them.
Once they say, "I don't believe in Santa Claus", do you really continue trying to convince them that he is real? They're just playing along with you after that and you've lost your authority. Honesty = authority.^