I'm a hardcore atheist but I have fun with the holidays. We never make the holiday about anyhting other than the fun commercial side of things. Christmas is about Santa and presents, family getting together and having a good meal. Easter is a spring celebration, about a bunny and chocolate and getting some spring clothing/toys. All holidays are a time to appreciate family and take a moment to enjoy what we have. We never really lie, we ask our daughter what she thinks and talk about possible answers to 'how & why' for things like Santa delivering presents all in a night, why the stores have all the Easter candy on the shelves, how a little fairy could possibly carry a tooth and what does she do with it. lol They are fun conversations and involve inventive ideas like bi-location, time travel, delegation of duties, etc. We never say for sure how things are, just give ideas on how things might get done. It's a game and one day we know our daughter will catch on and one day we'll know she knows and then she'll play the game for the twins so they can enjoy the magic of being a child too. There is such a small window of time when life is truly magic and all seems possible. If you're spiritual then use it as an opportunity to talk about faith, if your an atheist use it as a chance to talk about science and economics. Whatever floats your boat! If you're not going to celebrate traditional holidays then make new and fun traditions and celebrations.
You cannot avoid your child finiding out about holidays/celebrations if you plan on having them ever leave their home. lol Think about the level of commercialism in today's society! I definitely think that if your LO is your first then definitely you can avoid buying gifts until they are a little older (my sister is doing that). And once they are old enough to be aware then it's up to you as the parent to decide how you want to handle the celebration.. whether it is purely a religious event or only commercial or a combo of both. One way or the other though you will set your own traditions and that will become the norm for them. If it's really different from their peers though you will most likely have to discuss why it's different. We had to have a simple conversation with DD about what a church is and why people go there etc after an great-aunt decided to confront us about not going to mass at Christmas 2 years ago in front of DD1.
Anyway, blah, I'm babbling.. I'm so tired today. Last night DD1 got up in the middle of the night and accidentally tripped and cut her head open bad. I ended up taking her to the hospital to see if she needed stitches. They were able to use some magic glue because there was a straight margin on the gash. Hopefully my poor girl won't have a scar. Anyway, we didn't get home until the birds were up and then I only got back to sleep for 2 hour before the twins woke up. Meh.