DS is 9 and for a couple of years, he's been doubting that Santa exists, but we tell him that some children believe he exists, some children don't, and that's ok. I always make a big deal out of Christmas, and try to create a lovely family celebration as I have very fond memories of Christmas as a child and I want to do the same thing for my children. We are a Christian family and attend Church, Sunday School, etc and it's a very special time of the year.
MIL told me many times in the past that she always told her children - DH and his sister - that Santa doesn't exist as she didn't want to confuse them and didn't want to be accused of lying to them as they got older.
When DS (now 9 YO) asked her if Santa existed, instead of saying what we say - (maybe he doesn't, what do you think?) she actually answered 'No darling, he doesn't exist' and then she told me over the phone that DS was upset because we had lied to him.
IABU to be upset over this? She apologised and sounded very sorry, and I told her not to worry about it because she worries about everything and I don't want to cause any more damage/conflict especially at this time of year. But inside I am fuming.