Re: The power of Santa...
Well in your situation, where the kids know somethings up, probably sense your fear and loneliness, I see how they are asking questions! I would be honest with them. I would't tell them he has bullets flying at his head but I would tell them the things you believe about what he's doing in terms they can understand.
"he's in another part of the world, he signed up for the job and it means he has to be gone when they say, it is a dangerous job and mommy hopes every day that daddy will be safe, protecting other people can be a dangerous job, daddy took this job because he is a brave man and he wants to help people, let's spend time praying for/sending daddy good safe energy, etc. "
It seems to me like if a child senses and knows something anyhow the best thing to do is be honest so they know you're there for them, they can come to you, etc