The faces of adult characters who interact with the child characters are never seen in the Peanuts comic strip and rarely seen in the animated cartoons based on it. However, the presence of adults has been indicated in a number of ways.

As part of a series of Sunday strips from May 1954 in which Lucy joins a golf tournament, adult legs are shown in the strips from May 16 and May 23, 1954. and indistinct adult figures are shown from a distance, their faces not visible, in the strip from May 30, 1954.

The hands of a Dry Goods sales clerk are seen in the final panel of the strip from October 17, 1954.

The face of an adult doctor, drawn by Linus to accompany a story that he has written, appears in a Sunday strip which first appeared on November 8, 1964. The doctor is not drawn in Schulz's usual style but instead in imitation of the manner in which a young child draws.

Willie and Joe, soldier characters created by cartoonist Bill Mauldin during World War II, appear in the strip from November 11, 1998. The strip is mainly drawn in the style of Mauldin rather than in the style of Schulz. Adults can be seen in the strip from December 19, 1999 in an image taken from the 1851 oil painting Washington Crossing the Delaware by Emmanuel Gottlieb Leutze. Genuine photographs of real adults appear in two Peanuts comic strips. The Sunday strip from May 31, 1998 commemorates the June 1944 Normandy landings. It is made up primarily of a photograph of Dwight D. Eisenhower and men of the 502nd Infantry Regiment. A photograph of the Pulitzer Prize-winning World War II correspondent Ernie Pyle appears in the strip from November 11, 1999.

In early Peanuts strips before the mid-1950s, some adults were given speech bubbles, but were never shown. However, in later strips, they are neither depicted nor directly heard from. In the TV specials, their voices are almost never heard. When an adult speaks, the viewer usually only hears a trombone (with a mute in the bell).

Schulz said that grown-ups just did not interest him. The absence of adults also gives Peanuts a unique point of view, bringing the comic down to the level of children, and not children from an adult's viewpoint.

There are a few adults who are frequently mentioned in the strip - such as Miss Othmar, Joe Shlabotnik, Mr. and Mrs. Brown, Mr. and Mrs. van Pelt and Lucy's Aunt Marion - but none of them have been seen, and hardly anything is known about them.

One of the mysteries surrounding the strip for casual readers is the apparent lack of influence the parents have on the characters, due to their infrequent references. Aside from obvious signs they are there (the births of Sally Brown and Rerun van Pelt), the characters' households show strongly independent children capable of running their own lives, with their parents in the background. For instance, often the children do things which parents normally do. For instance, Charlie Brown has been shown making Lucy hold his hand while crossing the street, reading Schroeder a bedtime story, and helping Sally with her homework.

Peppermint Patty, for one, lives in a single-parent household, as she only refers to her father. Charlie Brown's mother is rarely referred to, and the parents of some later arrivals (such as Eudora) are never cited.

The only parents who have ever appeared in the Peanuts comic strip are Snoopy's parents who are, of course, not human.

Grandparents, in fact, are cited more often than parents are, especially in later years of the strip. Linus lives in fear of his blanket-hating grandmother whenever she comes to visit, while Franklin, in his early conversations with Charlie Brown, talks about his grandfather in the same respectful tone that Charlie Brown uses for his father.

The only Peanuts related media in which adult faces are seen, accompanied by understandable adult voices, are the movie Bon Voyage, Charlie Brown (And Don't Come Back!!) (1980), its television sequel What Have We Learned, Charlie Brown?, (1983) the mini-series This Is America, Charlie Brown (1988-1989) and the TV specials It's Flashbeagle, Charlie Brown (1984), It's the Girl in the Red Truck, Charlie Brown (1988), Snoopy's Reunion (1991), You're in the Super Bowl, Charlie Brown (1994) and It's the Pied Piper, Charlie Brown (2000).