Do you need to list out children’s names on the envelope?

We put the kids names on the envelopes. Any kid 18+ should receive their own invite. We put the names on the save the date envelopes though. I just didn't want to deal with bombarding questions on if kids are invited. Then when the invites go out, I'll have the couple on the outer envelope and then every name on the inner envelope. On the RSVP, it will say how many seats are reserved and a section to write in how many will be coming.

Etiquette says that anyone over 18 gets their own invitation, regardless of where they live.

If you have an outer and inner envelope, you put the parents' names on the outer and the names of everyone invited on the inner. Many people are not having two envelopes, though. In that case, if it's a family with younger kids, you can put "The Smith Family" to be clear that the whole family is invited. You can also put "X number of seats have been reserved in your honor" on the RSVP card so they know how many family members are included.

In your case, stick with sending each adult their own and there shouldn't be any confusion.