Impulse first appeared in 1994, during Mark Waid and Mike Wieringo's run on The Flash. The character served as a kind of quasi-sidekick to the Wally West Flash for years, although it would be about a decade before he would become Kid Flash, a name he took on during Geoff Johns's run on Teen Titans.
About a year later, in 2005, Allen would briefly replace Wally West as The Flash, when Wally retired from the role and left the present day to live peacefully with his wife and newborn children in the future. he was only The Flash for a short time, before he died and was replaced by Wally, who had been brought back to the present in a Justice League of America storyline.
Bart would return from the dead in Final Crisis: Legion of Three Worlds, part of the same over-arching story which saw Barry Allen return from the Speed Force and supplant Wally as the primary Flash.
A piece of key art features what appears to be a tablet or photograph with Flash and Kid Flash running together, the image identified by CBR as Wally and Bart, since the costume featured looks like Wally West's pre-Final Crisis costume.
It may not be Wally and Bart, since flashbacks in post-Flashpoint stories have tended to make Barry's costume look just like Wally's -- the key differences being that Wally's was often depicted as "shiny," usually had lenses covering his eyes, and featured the lightning on his "belt" coming down in a V shape rather than simply circling his waist.
Either way, the images give a lot of hints that some of Wally's pre-Flashpoint timeline will be explored in the upcoming "Flash War" story: a look at the Flash museum reveals celebrations of characters like Max Mercury and the Tornado Twins, as well as "The Life of Iris Allen." In the current continuity, Barry and Iris are not yet married and the Tornado Twins -- their children -- not yet born. Neither they nor Max Mercury have been active in DC Comics since 2011's reality-altering Flashpoint.
Oh, and whether or not Bart is the one depicted in that broken photo, that is absolutely a puppet verison of Bart (presumably compliments of Abra Kadabra) pictured at the bottom of the image, its face smashed in. And beside him? That's Savitar, the self-proclaimed God of Speed who only appeared in one major story ("Dead Heat," also by Waid) before being killed in a cameo during Johns's The Flash: Rebirth.
Savitar, then, remains one of Wally's most formidable and powerful villains -- one who required an army of speedsters from throughout time and space to stop him -- and he has not had a single story during the era of Barry Allen. That itself could lend to some tension between the two Flashes, as Wally could rankle under Barry's instruction, if the threat is someone (either Savitar or Kadabra) with whom Wally has more, or at least more recent and relevant, experience.
The bigger question, of course, is how Bart (Barry's grandson) will play into the story. Wally has memories from the pre-Flashpoint universe and can likely tell Barry how things are "supposed" to play out with his family. An appearance by Bart would have seemed like a pipe dream not long ago, but between the revival of much of the pre-Flashpoint mythology of the DC Universe, and the appearance of an evil, older version of Bart during the recent "Super Sons of Tomorrow" story arc in Superman, Super-Sons and Teen Titans, it looks very much like that puppet could be more than just a fun Easter egg for fans.
The Flash Annual #1, which kicks off the "Flash War" storyline, will be in stores on January 31.