There are lots of films where single men act as surrogate fathers, from the John Wayne flick 3 Godfathers to Annie, Curly Sue, Fred Claus, About a Boy, Role Models, Happythankyoumoreplease [yep], Kindergarten Cop, Big Daddy, and (kinda) True Grit. It's also a common trope on TV, in shows where the non-dad "dad" is related to the children in question, like Hangin' With Mr Cooper, Party of Five, Full House, or Gilmore Girls, and also where a lone man rescues a needy stranger (and himself in the process), as in Punky Brewster.
In the 2005 Disney movie The Pacifier, Vin Diesel plays Shane Wolfe, a Navy Seal turned temporary child minder. After failing to protect a government scientist working on a top-secret program that prevents other countries from deploying nuclear weapons, he's sent to protect the man's family as they've experienced some attempted break-ins, presumably in search of the secret program (which Wolfe needs to find before they do). After the scientist's widow leaves for Switzerland to open a newly discovered safety deposit box belonging to her husband and the hopelessly negligent nanny quits, Wolfe is left in sole control of five children aged from baby to teenager. Hijinks ensue.
Wolfe attacks his new responsibilities the only way he knows how: with military zeal. At first, the kids ignore his attempts at discipline, casting off their tracking bracelets and ignoring his six AM wake-up whistle. Meanwhile, he has no idea how to connect with them, assigning them numbers because he can't remember their names. "We do it my way. No highway." He blusters, to no effect. He rarely talks like a human being throughout the entire film, instead spewing a series of action man clichés. (When he forgets the baby at a ball pit, he runs back shouting, "I've never left a man behind!")
His tough guy persona pays off in the end, though, and he (surprise!) ends up being a positive influence on all the children. Among his achievements, he teaches the oldest, Zoe, how to drive, shows young Lulu and her Girl Scout troop how to stand up to bullies (top tip: don't run away when they say "boo"), and even takes over directorial duties of a community production of The Sound of Music (naturally).
The bad guys trying to steal the government program turn out to be the family's neighbors, the Chuns, formerly of North Korea, who actually break through windows wearing ninja outfits while doing karate. So very racist, and yet the incident demonstrates how useful kids can be, as Shane fights them using all manner of children's accoutrements, from baby powder to toys, and finally the children themselves help him out. The day is saved, however, by Lauren Graham (of course). Here, she plays school principal Claire Fletcher, who used to be in the Navy and who pulls out enough martial-arts moves of her own to stop the Chuns from preventing America from detonating nuclear bombs. (A worthy cause, if ever there was one...)
Although Wolfe becoming the perfect caregiver in two short weeks and Fletcher just happening to stop by with a can of whoop-ass wraps things up a little too conveniently, I appreciated this non-gender-conformist ending. It's worth noting though, that for a man to become a caregiver of children he doesn't know and still retain the respect of people around him, he has to be on some kind of military, humanitarian, or otherwise honorable mission: taking care of an orphaned young child or becoming a role model where a parent is too self-involved or mentally ill to do so. (Men who become caregivers and lose the respect of their peers are a whole other story, of course—expect more on the much maligned "manny" later in this series.)
Pairing him with a kid is an easy/lazy way to make a man seem sympathetic, without him having to take on the complications of a kid or fundamentally change his lifestyle. In some of these movies and TV shows, the lead becomes an adoptive father or father figure to the child, but more often, he moves on with his life; less invested in the kid now he's grown as a person and learned important lessons. I'm not sure why being a hyper-masculine tough guy (in The Pacifier, Kindergarten Cop, and parts of 1983's Mr. Mom, among others) is often so important, but perhaps it's an attempt to deflect the suggestion that the heroes of these stories might be gay, or worse, women.
There are far fewer movies and TV shows where women get involved in the life of a child they don't know; I suspect this would be seen as pathetic and a sign that a lady should grow up and get to procreating. (Allegedly immature and selfish women face a harsh backlash, whereas the man-child is just a charming little boy whose hair needs ruffling.) Sure, it's patronizing that when men take on childcare in a voluntary or professional capacity it's considered radical and inspirational whereas when women do it it's just a job. But it's also great anytime something traditionally viewed as a women's forte is acknowledged as the hard work it truly is.