So Gaia was the mother of Uranus and then had a son of Uranus? You guys are sick.
Anyway i find curious that Gaia (primordial earth, female) could be mother of the Uranus (primordial sky, male). I thought ancient greeks were machist patriarchal indoeuropeans.
According to the Theogonia: (my translation) "Gaia first gave birth to Ouranos, equal to her* so that he could perfectly cover her/cover her from everywhere"
Re Gaia as the first mother**, well at the time she is the only female deity, so naturally new children will come from her, either by joining a male deity or without such need (as in some cases with Gaia; eg Ouranos doesn't have a father).
Gaia is the first of the created things that can give birth, but isn't the oldest of things in the Theogonia. That order goes: Chaos--- Gaia --- Tartara (Tartarus) --- Eros. Then begin the children of Gaia, along with other stuff, like Erebos (Erebus), Night,and the Night creates Day when she is mixed with Erebos. Then comes Ouranos, and then the Titans, who are named thus because they were trying to flex their bodies inside Gaia where Ouranos pushed them back to cause they were jerks. Later they take revenge, with Cronos (Saturn) castrating Ouranos, and Aphrodite is born out of the sea foam created around the cut genitals of Ouranos - which is why her name is that, it means "risen/rising from the foam".
Then other stuff. And later on the Titanomachia.
It is a great read ^^
*It is not clear if this presents Gaia and Ouranos as flat surfaces, or that they have different shape so are "equal" but the latter is surrounding the former anyway. Moreover, Gaia is the ground/earth itself, full of openings.
** Technically, Chaos also creates some things. Namely Erebos and Night. Those aren't easily tied to gender, though, and neither is Chaos. Well, Night is feminine in greek, and she does give birth to other things following a mix with Erebos, but Erebos (like Chaos) is neutral in greek, neither masculine nor feminine.