Superman & Lois - now ALL seasons

I'm still going through the pilot, but I'm a little off on one thing...

I thought Jon was the only biological child and the other child was the one they took with the from the planet that was destroyed. Was everything just retconned on us?

Am I asking a question that will be answered by the time I'm done with this?

I'm pretty sure the kid from Krypton was their only child and then the Crisis rebooted them with 2 teenagers.