4) Bart Allen
Bartholomew Henry “Bart” Allen II is part of a complicated lineage which includes Barry Allen and Iris West as paternal grandparents and Meloni Thawne and Don Allen as parents. For most of his superhero career, Bart is the new Kid Flash to Wally West’s grownup Flash. He eventually joins the Teen Titans and then, when Wally West apparently dies in the Infinite Crisis storyline, Bart grows up and takes on the mantle of The Flash.
This version of Kid Flash also appears in multiple other storylines, including Blackest Night, Infinite Crisis, Flashpoint and The New 52. One of the interesting things about this character is that he suffers from hyper-accelerated metabolism, causing him to age faster the more he uses his speed force powers.