spoilers for TCW season 7
In season 7 of The Clone Wars, it is established that, not only did Rex know about Anakin and Padme, but he helped them hide their relationship. By that point in the timeline, Padme is visibly pregnant. Obviously, Rex would know that she is pregnant with Anakin's child(ren). However, during the events of Revenge of the Sith, Rex and Ahsoka are fighting for their lives and largely unaware of what is happening. By the time they've survived, it is implied that the events of Revenge of the Sith have ended. Padme was made to still appear pregnant at her funeral, so, if Rex wasn't in contact with Obi-Wan or Bail, he wouldn't have known that she had actually given birth. It doesn't seem like he did interact with either of them before they both went away to raise Luke and Leia.
So, did Rex know that Padme had given birth before she died? Or did he believe that her children had died with her?