Outer envelope: Mr. and Mrs. Charles Smith
Inner envelope: Charles and Nancy Smith
or Charles and Nancy Smith and children
Outer envelope: Ms. Nancy Smith
Inner envelope: Nancy Smith and Guest
If you want the children to attend (or don't) you must specify on the inner envelope. Be specific.
If you want a more complete and detailed list of the guidelines in addressing envelopes, it's better to search for it online. There's a different addressing for outer and inner envelopes so it can be a bit confusing. There are many wedding envelope addressing articles online. For more wedding envelope tips, just check the related link I added below.