I've had this same problem with my hubby's grandmother, aunt and father (basically, the in-laws) except my problem was that they were trying to impose their racism on my kids...
First thing I did was threaten to not let them see my kids..this worked with all but my ignorant FIL who lacks the common sense not to say the "n" word every other sentence..
so, sadly enough, I had to introduce the word "ignorant" to my 3 yr old and explain it's meaning. I went a bit further and explained how some people are unhappy and wish to spread their sadness to other's. I told her the "n" word is only said by those type people. Next time she heard FIL say it, she said to him, "pa butch..I wish you weren't ignorant..maybe you wouldn't be so unhappy". I about died...hubby laughed. I'm not sure she completely understood what I was telling her, but one day it'll all make sense..i hope.
Recently, she made the statement to me that , "one day God will come get ALL of us and take us to heaven, Mommie..but he won't come until I'm real big..will he?". I was a bit confused..I had a 16yo niece killed in a car wreck last year and thought this may have been the reason for the comment, but I thought it odd this sentence just come up out of the blue. I asked her where she heard that and she told me hubby's aunt told her all about Jesus and the devil. Over the course of a week, my 3yr old brought this topic up several times. I could tell she was worried. I asked aunt about it..she said, "I was just teaching her about Revelations!!!". Infuriated me. Aunt is a religious finatic (yeah the same one that's a racist)..I'm a Christian, but I'm big on protecting my kid's innocence and I think religion is confusing enough for adults w/o a 3 yr old having to worry over it. As politely and tactfully as I could, I told her I did not appreciate her pushing her religious beliefs on my child and confusing her. I went on to explain that a child lacks the ability to differentiate "someday" from "tomorrow"..and to a toddler, the thought of some man she's never seen coming to take her from her mommy is terrifying..even if it is God. The conversation didn't go well, so I ended up telling her that she is NOT to discuss religion with my kids, period. As far as I know, she hasn't since.
I don't understand adults who wish to steal a child's innocense..to introduce evil. I think it's an unconscious jealousy that the child has a happiness that an adult can't ever get back. I would never prevent my kids from seeing those they love, but I did threaten it to the adults..and I made them think I meant it. It worked for me.