In reply to Jeanette L, part of the problem here is that there IS a difference between sins. Chubby or boasting grandparents don’t bother me nearly as much as fornicating grandparents! The original poster was very clear that the children see their grandparents frequently, just not with the significant-other-of-the-month. She is exercising her parental duties and rights, not punishing the grandparents for their immature behavior.
Our society has made obesity a worse sin than cohabitation. We, as Christians, can’t blur those lines and say “well, everyone sins, so the specific sins don’t matter.” Our children will pick up what we say and do on these matters, and, yes, they need to be shielded from some of the worst examples, especially in their immediate family, while they are young.
Quick example of misguided all-sin-is-equal thinking. A good friend of mine was stuck listening to an argument between her sister (pregnant from a one-night stand) and her mom.
Mom: “What the heck were you thinking?!? Why didn’t you at least use a condom or something?”
Daughter: “MOM! I’m Catholic, we don’t believe in birth control!”
Mom: “WE DON’T BELIEVE IN PREMARITAL SEX, EITHER!”