Continuity mistake: When Mom gives Molly the donation box she writes "Sunnyside" on only one side of the corrugated box. When the Sunnyside box is in the car and also when Mom carries it to the daycare, there's printed red text (name, contents, etc) under the hand hole at the adjacent side of the box, but when Bonnie's Mom carries the box into the butterfly room that printed red text has vanished (NOT the handwritten "Sunnyside"), then it reappears when the kids go to recess. (00:19:25)
Continuity mistake: When Bonnie gets the burger out of the microwave the door is left wide open. As the shot changes the door is shut. (00:34:10)
Answer: Yes, he is. He can be seen wearing the same black t-shirt with a skull motif that his younger self wore in the first movie and Pixar have confirmed that the character's intended to be Sid.
Tailkinker ★
In addition, they are voiced by the same person.