For the record. My kid doesn't believe in Santa clause and he is 9. But he still asked me if we can leave out milk and cookies...,cuz he knows I'll get up and eat and drink and he'll wake up to a couple of extra gifts under the tree that have santas name on them.....he's no dummy.
So your kid is pretending... you going along with it is not lying to your kid. It's harmless fantasy... I loved it as a child. Some people will still think it's taking away from Jesus, which I disagree with. However, I wasn't talking about your particular scenario, in fact, I have spoken out that if we make it clear what is fantasy and what isn't, it's okay to pretend. Many parents don't tell their kid it's pretend but that in reality, a big fat man wearing a suit literally travels the world on Dec. 24th and goes down the chimney delivering presents to good boys and girls. They make excuses for why they bear false witness.
It also wouldn't make the children a dummy for believing it... I mean, they are just believing the people in this world who love them the most... For this reason, it's important NOT to lie to them... yes, pretend and play with them, but don't lie to them is all I've been saying. =/