According to DCU Rebirth #1, the Justice Society was a covert team of heroes who helped bring about the end of WWII and then were accidently banished from reality by Johnny Thunder during the subsequent McCarthy hearings. Presumably, they disappeared in 1951 (though it could have been as late as 1956). When the JSA returns later this year, I suspect that they'll be in their mid-30s, roughly a decade older than the League (or maybe only five years older, if the New 52's five-year gap has expanded to ten years).
The catch is that any children they may have had would have been at most ten years old at the time of their disappearance. If they were left in the past, they're be approaching retirement age today; and if they're brought to the present with their parents, they'd still be children.
So how to bring them back?