I read about this idea several years ago, past the time when my sons were non-believers:
Only one gift per child comes from Santa. If circumstances in your life (layoff from work, mounting debts, etc.) make it difficult financially to purchase a number of gifts, at least you've set the precedent that Santa only brings one gift. Explaining to your child that your family situation precludes tons of gifts is easier if they know that Santa only brings one gift and the rest come from the parents.