no matter who is around, but especially if you're going to be eating a big meal with kids, try and refrain from talking about how "bad" you're being or referring to how much food you are eating or the foods themselves as having morality (good v bad).
when denying food "too much sugar hurts my stomach" vs "I'd have to run miles to work that off" makes a big difference with how everyone, but especially kids, form a relationship with food and holidays.