First, if the child(ren) are over 18, they should receive their own invitation, even if they are still living at home.
Obviously, if you do have an inner envelope, the names of all those being invited, including children, should be listed there, not on the outer envelope. But if you are only sending an outer envelope, then try some of these approaches:
If you know all the names of the children, list them on the envelope, like such:
Mr. and Mrs. James Smith
Lisa, Aaron and Michael Smith
If there are too many to fit on one line, it is ok to list the additional names on the next line, like such:
Mr. and Mrs. James Smith
Lisa, Aaron, Michael
Susan and Joseph Smith
I have also seen the children receive their own invitation, especially if there are quite a few in the family. This is a pretty rare occurence, but visually speaking, the appearance of the envelope looks much better than having 6+ lines of peoples names and addresses.
One of the very last options is to address the envelope with "and Family". This is very much frowned upon by the etiquette police when addressing wedding envelopes. Since you are going through the work of addressing them, you should spend the time to address it to everyone being invited...which means finding out the names of all the children in the household. But I know how difficult this can be, especially if there will be a large number of families w/children being invited.
Lately, etiquette has been given a back burner on some of these ocassions, becuase it just isn't feasible to do it like we were living in the early 1900's. Times change and so do customs and etiquette. What works for one may not for another, but isn't that why life is so grand?
