The other day my 5 year old told me she hopes our state makes it legal for girls to marry girls when she's grown up so she can marry her best friend. In the next sentence, she told me she wished this best friend was her sister. To kids this young, love is love is love. They don't see that the way mommy loves daddy is different from the way mommy loves grandma, so they don't question the way mommy loves any of the adults in her life. As long as you're not referring to them as your "lovers," the kids don't have any incriminating knowledge to blurt out at church functions. And hopefully by the time they get old enough to be aware of sex, they already understand that these relationships have a solid foundation of love and respect (I would hope -if you're swinging you might want to shelter them from that for a few years more!).
My husband worries about our kids too. He wanted to bar C from being around them. I chose to halt the intimacy in order to keep C in a healthy relationship with me (not hidden from my family). Now my husband realizes that it's better for the kids if we're not treating C differently from other friends, so my kids know him as a man I sometimes hang out with.
Married to a monogamous man 15 yrs, mother of 2, dating C 3 yrs, and in a romantic friendship with L more than 20 yrs