I think telling my kids things for their enjoyment is ok. I don't believe me or my siblings were hurt by our parents given us the santa myth and I also feel it was an important life lesson to discover santa didn't exist.
How would you feel if you did have a suprise party? / No, but would you like me too? / No, but would that be ok for a future birthday?
What do you think I would tell you if you asked me that and I was planning a surprise party? Or if I wasn't?
You don't have to answer all their questions. Personally, I'd say, no, I don't like surprise parties, so I'm not going to plan one for someone, but for the sake of argument, I'll pretend I might.
The truth is that not every lie is a problem.