Each one of these kids knows what it's like to be unwanted—they've all been tossed out into the water by an unloving parent or grandparent. They regularly have treading water contests to see who can stay above H2O the longest or survive in the wilderness. As it is, they provide support for one another when their families aren't nice.
Perseus and Lugh get along really well, since they have similar backstories. Both of their parental units had affairs that their maternal grandfathers didn't like, and both were cast out as babies. They started a club called "Mythological Grandfathers are the Worst"—it's easier for L and P to say that now, since they both bumped off their grandpas. Small world, huh?
This ancient king of Persia was a real guy with a fantastic backstory—or so he claimed. The Median king Astyages married his baby girl off to a prince named Cambyses, but Asty had a bad dream that the resulting baby would kill him. Cyrus ended up being raised a shepherd, instead of a prince, but he did become a royal again once his grandfather, no longer afraid, discovered he was alive. Eventually, Cyrus became king after—what else?—revolting against his granddad.
These twins were born of the Roman god Mars (lord of war) and Rhea Silva of Alba Longa, which is in Italy. Rhea's uncle, Amulius, was afraid these cute babies might overthrow him one day, so he tossed them out. R & R were nursed by a she-wolf and picked up by shepherds, though, and raised to be handsome young guys. When they got old enough and discovered their heritage, they, indeed, bumped off their great-uncle and put the rightful king, their grandpa, back on the throne. Then, of course, Romulus founded that great city of Rome.