Saw this question on Reddit. My favorite answer:
"In The Santa Clause (yes the Tim Allen one) it always bothered me as a kid that the parents don't believe in Santa Clause, but they never brought up the fact that there are presents on Christmas morning delivered by Santa that weren't purchased by the parents.
If Santa existed in these movies then he would've delivered presents to their kids, so why wouldn't they wake up on Christmas morning and think "hmm.. I didn't get Tommy this skateboard. I guess Santa is real!""