Unless your children are infants and toddlers, it is a mistake to assume that they do not know about your lifestyle or they will not find out.
If you are attempting to teach your children traditional values, don't you know they will go more by your example, than by the things you have said?
If they do not know, it is highly likely that they will find out, and then you must either deal with their feeling of being betrayed, or you tell them of the virtues of your lifestyle.
I know nothing about you or your wife, but I do know children and human behavior. Kids are fantastic when it comes to overhearing and seeing things they were not meant to see.
One more thing. If you are so totally sure that swapping is a good lifestyle...why don't you tell your children???