[all] Would it be possible for there to be a demigod child of Helios?

Assuming if someone could revive Helios again to full power + corporal form, then yes.

Medea. Was a daughter of Helios I believe

Phaeton was a thing, so yes

I think in Percy Jackson's greek heroes there was a demigod child of helios that died driving the sun chariot.

Helios has faded in the series so we won't be seeing a demigod from him. A legacy is possible.

No, he's faded since the Roman times. But before that yes, Phaeton is a son of Helios.

Well if Ida exists, then sure why can't a Helios child/legacy?

Main thing against it would be how awkward it is from a storytelling perspective. You had the main character go through that tragic journey to convince Helios to fade for good and that he will honor the fallen god forever. And then a demigod child of his just pops up all of a sudden.

Yeah

Phaeton

But wouldn't they be called a Demititan?

It is possible in a logical sense, since other Demi-Titans are known of in-universe. However, not exactly possible because of some events in ToA

I mean he might be retired somewhere in the mythological world, just hanging out. Then he seems some beauty sunbathing and pops down to break off a piece of that.

I heard that descendant of Helios have bright golden eyes.

He's kind of dead now, but Phaethon existed so it's entirely possible.

Yeah and he turned into tar or oil or sum

That depends, can the Fates have children? I mean, Clotho is a good contender since she creates life.

I hope so