You can always pawn the kids off to family members who can have "the talk" with them-
My daughter, who is almost 8, was spending a few days at her Aunt's house several weeks ago. Now, I haven't had any discussions with my daughter about "it" yet, or anything even remotely related to "it", other than explaining the differences between her bits and her baby brother's bits. So, a day or two after she gets home from her Aunt's house, she throws me some attitude and sass....so I ask her what's wrong, and she says "I must be on my period"....uh, hibbity WHUH???? After I pick my jaw up off the floor, she tells me that Aunt Holly told her about periods. I'm like, "Ok, what did Aunt Holly tell you?" Her response:
"Well, Aunt Holly was really yelling at Uncle Paul one day, and then she snapped at me, too, but I wasn't doing anything wrong. She apologized to me later, and said it wasn't my fault, that she was on her period. I asked her what a period was, and she said that when a woman is on her period, she eats everything in sight, and she gets really mad and mean and yells at people for no reason."
I guess that's a good enough explanation for now.