The stamp that says "Cancelled", disappears on Tommy's diaper moments after it is put on.
In the first season, Chuckie's mother is referenced several times as if she was alive, In the episode "Real or Robots" as Stu tucks Tommy and Chuckie into bed, he even mentions Chuckie's "Mom and Dad" coming to pick him up in the morning. It's later revealed that Chuckie's mother had died sometime before the series started, she is never shown in any episodes, other than in flashbacks.
When Tommy for the 2nd time tries climbing up Stu and Didi's bed, Stu's hair is orange, much like Chuckie's. But in the next shot, his hair is back to normally purple.
Tommy and Chuckie's screaming from Stu thinking he was a robot but just sleepwalking, might have woken Didi up. Or, she could be a heavier sleeper than most people.