Even convicted abusers have admitted being surprised by how easy it was to get a child to keep their abuse a secret. Secrecy is, obviously, essential for the abuser to victimize.
Many abusers will groom children by testing them to keep small secrets (“don’t tell mom I gave you this”) and then take it further. By teaching your children at an early age that secrets from mommy/daddy are not allowed, you are reducing the risk for this ploy to work on your child.
A surprise is one thing – because the end result will be the person finding out. A secret is not allowed. Lead by example and make sure the child and your friends/family know that secrets are not allowed – even if it’s just about sneaking some cookies before dinner.