[It's more the question that makes Bart pause than the fact that Wally had signaled for him to stop and slow down on the information front. The silence doesn't last for longer than a few seconds though before he's back to grinning at the older teen.]

That's what I said. About the grandson part. Not the Kid Flash part. Don't wanna reveal too much about the future, you know? [He's skirting around the answer a bit, but if pressed Bart figures that he can say that Wally isn't Kid Flash in the future. It's the "why" that he doesn't want to have to say.]