How do you handle prayers or the saying of grace at meals with extended family?

I have three sons who I am raising with the goal and purpose of teaching them how to be decent human beings. Giving them the tools they need to achieve that; respect, tolerance, love, a thirst for knowledge, etc.

However, my family and my ex's are both religious in that at family get togethers, they will request that we all say grace before the meal. Until now I have bowed my head along with them and just not participated in the prayer. But now that they are older, my children are asking why we do this if we don't pray.

Part of me feels like we are respecting them and their beliefs by at least bowing our heads. But then I wonder if I am sending my boys the wrong message by not standing up for what I beleive in, which would no prayer and thanking the preparer of the meal and those that worked hard to earn the money that paid for the food that made the meal.

Maybe I'm making too much of this... I can do that sometimes. But, thoughts?