Huh? What does this have to do with your point that "bearing false witness is okay as long as there isn't any malicious intent" or my rebuttal to your point?
I don't think that a small child would understand the terms 'pretend' or 'fiction'. I hardly think that a parent telling their kids about Santa is bearing false witness. A lot of how a parent would handle this would depend on their level of spiritual maturity. If a parent suffers a guilt complex about every little thing than yeah, no Santa, Easter Bunny, tooth fairy or trick or treating. A lot of happy childhood memories would not happen. There are exceptions but the reason that a parent would not let a child experience these things probably comes out of fear and guilt.