In a lot of ways, Hercules is pretty lucky. In most Disney movies, one or more parental figures die a horrible death so that the hero can learn to grow up on their own. In Hercules, the titular tyke's parents remain among the living for the duration of the film, and seeing as they're gods, probably forever after. Even when Herc is kidnapped and robbed of his godhood, he still ends up with his own humble but loving Ma and Pa Kent for guardians.
But wait, if they weren't dead, why did Zeus and Hera leave their darling child alone with a couple they'd never met before?
With impeccable musical timing, the Gospels explain that Zeus and Hera were too late to save Hercules from becoming mortal. Since he was no longer a god, Herc was not able to rejoin his family on Mount Olympus. It seems extremely arbitrary and unfairly harsh, but you sort of accept that's just the way things are with Greek gods.
But the real kicker here is that Zeus and Hera make absolutely no effort to contact their long lost son. For years, they let complete strangers raise Hercules without intervening. It was like their kid was a baby bird, tainted by the outside world and no longer lovable. Worse, Zeus and Hera knew someone was after their son, and they did nothing. Baby Hercules was kidnapped from their home and nearly killed, but his parents did absolutely nothing to prevent the killer from coming back and finishing him off. We the audience know that Pain and Panic decided to tell Hades that the job was finished, but nobody else in the movie knew that. It'd be like learning the Subway guy is chaperoning at the high school prom but letting your kid go anyway because the dress you bought at Forever 21 is non-refundable.
When Hercules finally learns the truth when talking to the uh, giant statue version of his father, Zeus just sort of brushes this revelation off as lighthearted fun.
A "SURPRISE!" should be saved for a birthday party, or maybe as an excuse when you're caught using your boss' bathroom. "Abandoning your son for a decade and leaving him open to attack from unknown forces that already made an attempt on his life" is not a "SURPRISE!" It's not even an "OOPSIES!" or a "MY BAD!" This warrants nothing less than a call to the God of Child Protective Services, who I have officially dubbed Abusciles.
Remember, even though Herc was not allowed on Mt. Olympus, we see no reason to believe that gods aren't allowed on Earth. After all, Hades skulks around on the surface all the time. Oh, and about Hades...
The slick, fast-talking God of the Underworld is very likely the most popular character in Hercules -- and for good reason. Voice actor James Woods does a fantastic slimeball, and his sneaky snark and sporadic flare-ups made Hades one of the most memorable/lovable villains in the Disney canon. But for a supposed immortal deity, the guy is kind of an idiot. Hades, not James Woods.
The evil plan starts out well enough. Hades goes into a deep dark chamber of his own personal hell and plucks a special serum that can rob the victim of their godhood.
Where he got that immortality-killing potion and why there was apparently only one vial in the universe is kind of besides the point. We accept it as the bare-minimum dastardly plot. The end game, by the way, is to murder his own nephew, an infant still soiling his divine diapers.
In a certain sense it's something of an easy job, after you manage to kidnap the kid from Olympus, which apparently has no God of Home Security. The only problem is, Hades sent these two assholes to do his dirty work.
Pain and Panic are two of the most inept henchman in Disney history, but for some reason they're constantly getting work from Hades. When their boss called them in the room to get in on Operation Kill GodBaby, they couldn't even get down the stairs without tripping and impaling one another.
What about seeing these stooges falling all over the place makes Hades think "I should trust these guys with the delicate and risky task of nepoticide"? When you're a leader you do have to delegate, but the important part is delegating to the right person. There are presumably tons of other potential hitmen out there, including plenty of mortals who owe him favors (like Meg). Waiting for electricity to be invented and hoping Hercules might stick a fork in a light socket would be a safer bet than sending his two boobiest boobs to do the job.
When Pain and Panic inevitably fail and leave Hercules alive and mortal but with some leftover godlike strength, they pledge to keep it a secret from their quick-tempered shift manager. And it works! The lie isn't exposed for almost two decades, when Hercules is already established as a celebrity hero across the land.
Funny, considering Hades should have known something was amiss immediately.
As shown in the movie, the souls of the deceased float right in front of Hades as they come into the underworld. As the steward of the dead, that's sort of his whole thing. It's a big job because people stop living on a pretty consistent basis, and Hades even admits that he's swamped most of the time. Even so, you'd think that Hades would take special time to gloat over the sad baby ghost of Hercules when it made its way through his domain. After all, Hades seems very tempted at the possibility of owning the soul of his brother's son at the end of the movie, when Hercules strikes a deal to save Meg.
You're not supposed to think too much about Disney cartoons, but the characters in the movie should at least think a little.