After becoming the Flash following the death of his mentor Barry Allen, Wally West ended up meeting and falling in love with Central City reporter Linda Park. The two eventually married and Linda even became pregnant with twins. But due to circumstances out of their control, their children, Jai and Iris, have gone through an absurd amount of reality-bending turmoil in their young lives.
Even though both speedsters are still adolescents, Jai and Iris have been wiped out of existence twice, before finding their way back into the core DC Universe.
WHO ARE JAI AND IRIS WEST?
Wanting to motivate Wally to be a greater superhero, Flash's former friend-turned-enemy Zoom attacked Linda and used his powers to cause a massive blast of energy, causing a miscarriage that cost her and Wally their potential children before they could even be born. But when Zoom became involved in the civil war that broke out between the Flash Rogue's gallery, Zoom attempted to travel back in time and actually kill Linda in the attack as well. Wally followed after him and was able to actually get ahold of Zoom. Using the future Zoom as a human shield, Wally was able to change the past and save Linda's pregnancy. In the present day, Linda almost died going into birth, but successfully gave birth to a son and daughter.
Naming them Jai and Iris, Wally initially intended to somewhat step away from his role as Flash to raise his children. Wally didn't get much time with his family, however. During the events of Infinite Crisis, Wally was forced into the Speed-Force during his battle against Superboy-Prime a few months later. Linda refused to allow him to go alone - grabbing onto Wally and bringing their children along for the ride. While the West family eventually returned, the Speed-Force accelerated Jai and Iris' aging. This meant the infants quickly grew into adolescence and even developed their own connection to the Speed-Force. While Iris had superspeed like their father, Jai could instead use his connection to the Speed-Force to accelerate growth in his muscles, giving him temporary enhanced strength.
WHAT HAPPENED TO THEM - AND HOW DID THEY COME BACK?
Their connection to the Speed-Force risked aging them too fast prematurely. It even briefly turned Iris into an adult with full control over her connection to the Speed-Force, until Wally was able to cure them. Jai even lost his powers during Flash: Rebirth, when Iris had to absorb both of their connections to the Speed-Force into herself to save her brother. While this leaves him mostly powerless, his sister can still lend him parts of her power so he can briefly have super-speed too.
However, both of them were seemingly wiped from existence after the events of Flashpoint reset the DC Universe. The Post-Crisis Wally West would eventually make his way back to the new DC Universe during the events of DC Rebirth and was broken-hearted to see that his wife no longer knew him and that his children were never born.
Wally was eventually called upon by the mysterious Tempus in Flash Forward to help deal with a broken world from the Dark Multiverse. After traveling across both the main DC Multiverse and the Dark Multiverse, Wally ended up in a false reality created by his fear of never finding his children. In this place, Jai and Iris were trapped alone on a dark world, hoping their father would save them.
Learning that the world's connection to the Speed-Force meant it wouldn't fade away like the worlds from the Dark Multiverse are meant to, Wally initially refused out of fear of destroying his children once more. But Tempus revealed the truth about the world: unless Wally embraced the power of the Moebius Chair -- essentially wiping his personality in the process -- and destroyed the world, the entire multiverse would be in danger.
Wally ultimately agreed to the plan, on the condition that Tempus uses his powers to save Jai and Iris from the world as it was destroyed. As Wally fused with the chair, Tempus completed his side of the bargain and rescued the pair - taking them to the core DC Universe and leaving them with their mother. The act gives Linda her memories of the previous reality back and reunited the children with their mother.
With Wally poised to be a major play in the DC Universe going forward in the pages of Dark Nights: Death Metal, there's a good chance that his children returning to Earth could give the Flash family another shot as helping save the multiverse.