Alan Ball’s directorial debut “Towelhead” tackles the disturbing topic of a 13-year-old girl’s sexual awakening and abuse. The subject matter is unsettling because it involves a child, but the presentation remains uncomfortably erotic, perhaps because Summer Bishil — the actress playing the central character — doesn’t look like a child.

Because she wasn’t. Bishil was 18 when the movie was filmed, which doubtless made things easier on everyone involved. As an adult, the producers needn’t worry about on-set tutors or doting parents and could explore the sexual scenes more starkly.

Although sexual situations involving teens are prevalent in movies and TV, depictions of teenage sexuality are rarely child’s play — primarily because actual teenagers seldom play those roles. But do filmmakers push further, even subconsciously, precisely because they’ve hired older actors? And is Hollywood’s exploration of teenage sex skewed by the fact that those fictional teens are really adults, who behave and carry themselves differently than most authentic teenagers would?

In television, this is hardly an academic exercise. Primetime dramas are filled with precocious teens, brought to life by actors in their late teens or 20s. This includes the stars of such series as the CW’s “Gossip Girl” and “90210” — who look 15 or 16 in the same way that I look like Brad Pitt.

In Showtime’s “Californication,” the central character played by David Duchovny has a tryst with a girl he meets in a bookstore. He later discovers she’s 16, although the actress playing her (Madeline Zima) is now 22 and looks it. So he slept with a teenager who looked like an adult, who was in fact an adult playing a teenager.

Then there’s Ellen Page, who was four years older than her character in each case when she played a pregnant 16-year-old in “Juno” and before that a 14-year-old who turns the tables on a pedophile in “Hard Candy.” Apparently, being 5’1″ means never portraying anybody old enough to vote.

Casting age-appropriate performers raises its own issues, such as the controversy over “Hounddog,” which caused a stir at the Sundance Film Festival over a rape sequence involving Dakota Fanning, who was 12 at the time.

It’s no wonder producers prefer dealing with older actors. For starters, those actors have had longer to hone their craft. Child labor laws also limit the number of hours a minor can work — a buzzsaw CBS ran into last season even with an unscripted program, “Kid Nation.” Such restrictions can add time and money to already-stressed scripted budgets.

The Screen Actors Guild — which has more than 5,000 members under 18 — has strict guidelines in place to protect them. In addition to curtailing work time, they include ensuring parental access, along with educational and dressing-room requirements.

“It is not uncommon for producers to cast and employ actors over 18 who can portray minors because, for example, they are not required to conform to the on-set educational provisions that are required for actors under age 18,” Pamm Fair, SAG’s deputy national executive director, explained via email.

Putting kids into sexual situations also tends to be thorny. Yet writers and directors love telling edgy coming-of-age stories, and networks welcome series featuring school-age characters — hoping to connect with coveted younger demographics.

Granted, employing older actors as teens is hardly new. Anybody who saw “Grease” might recall how the “students” at Rydell High all looked about 30. But because scenarios have become more explicit, the bar on what feels inappropriate (as with every other content taboo) keeps being reset — and appears to be racing ahead faster, seemingly, thanks in part to the actor-character age disparity that frequently exists.

Contemplating this topic brought to mind the early Woody Allen movie “Bananas,” where a small country’s new dictator rattles off a list of insane proclamations, among them, “All children under 16 years old are now … 16 years old!”

Hey, we get it: Life’s simpler when the kids aren’t really kids. Still, here’s a question for filmmakers before they wade much deeper into this swamp: Would you want your own children participating in such scenes if they were anywhere close to the age of the characters as written? And if the answer’s a big fat “no,” is it really less offensive — other than making your job easier — if the actors involved can go out afterward and buy their own beer?