4 outdated manners today's parents don't need to teach their kids

The etiquette territory "that changes the most quickly tends to be the manners around communication," Senning said.

For example, if you take a look at a 1920s edition of an etiquette handbook, there could be a whole section devoted to exchanging calling cards.

These days, Senning said, calling cards are largely obsolete — and many parents are instead concerned with how their kids are interacting with other kids on social media.

Instead: As Ana Homayoun, author of the forthcoming "Social Media Wellness: Helping Teens and Tweens Thrive in an Unbalanced Digital World," told The Washington Post, parents should help kids understand why they're posting or sending something on social media, so that they can make more informed choices.

Both Pachter and Senning said this is tricky territory, too. Only a few decades ago, you'd always have your kids call your friends Mr. and Mrs. Smith. Today, some of your friends might prefer it that way, while others might prefer Bob and Deb.

"It gets a little confusing," Pachter said.

Instead: If your kid isn't sure how they should address another adult, Pachter's advice for them is to err on the side of formality. "You can always be a little more formal and work your way down," she said, "but it's a lot harder to work your way back up."

Here's a tricky area that Pachter pointed out.

For example, maybe at home, Dad does carry the grocery bags for Mom. That doesn't mean that at work or school, your son should insist on carrying a woman's bags — she might consider it insulting or awkward.

Instead: Pachter's general rule that she recommends teaching kids is "help anybody who needs help" — regardless of gender.