How do you know your kids believe in Santa Claus?

[Trinidading3]

I asked my DS 10 yr old if Santa is coming via the kitchen window this year? He said "I don't know" This brought tears to my eyes as I really thought this year would be the year he says "Santas not real" ....I remember my other son at this age holding me hostage to tell him the truth as his friends said it's not real....

We just don't talk about it, but at 8 if she asked me outright I would tell her. She did a lot when she was 5 or 6 and she was evasive, then a kid in class with an older sibling told her santa wasn't real. I think she knows but doesn't want to spoil it. She's not daft