I am a human being and, as such, am a sexual being, just like anyone else. I usually ask them if they are openly sexual in front of their children. I simply smile and then explain such is the same for most in the BDSM lifestyle. We don't go around wearing leather training collars, leashes and fetish attire in front of our kids or out in the general community. This is something between only my partner and I or shared in an environment of consensual adults with similar tastes, such as at a play party.
Society has such a warped view of what is normal and acceptable vs. what is abnormal.
They fail to understand that in the realm of adult consensual sexual expression, there are no rights or wrongs, merely preferences. The word adult is paramount here. As with all parents, we practice common sense and protect our children from things not appropriate for them. I feel it's important that they see true caring between adults, to see how a man treats a woman or a woman treats a man as they will carry this with them into their own future relationships. Like it or not, they learn gender roles and how to treat one another from watching the significant adults in their life.