More specifically, Uranus was created by Gaia (Earth), so is technically her child, but he didn't have a father so not really in the traditional way. Uranus had many children with her, the most important of the lot being the original titans (including Kronos/Chronos/Saturn). He didn't want them to take over, so cast them down. Gaia got sick of it, armed the boys, and let them take out dad by murdering and castrating him. ...the hippy nature of Gaia is weird, considering all this.
I love mythology terribly, but I'm having a hard time getting over the weird old man Uranus. He'd more accurately be portrayed with some laurels or sky-type characterization...or hell, just with little Xs in his eyes, seeing as he's dead and all.
The exclusion of Pluto actually works pretty well, since Hades was secluded from the others due to the nature of his job and all. He should have some more detailing to show him as his mythological counterpart though.
Edit: Crits aside, I do think this is a wonderful design. I'm just so crazy over Greco-Roman mythology that I might dwell to much on the crits. Sorry. Great work overall!