Info dump post, because that statement is not quite correct.
Jaeaherys' kids are 2 (Daenerys) and 0 (Aemon) by the time you come back (early 56). You won't see further dragonriders from that line for another 10 years at minimum, and probably for even longer.
But there IS another dragonrider.
Aerea rides Balerion
Jaehaerys rides Vermithor, a powerful dragon, too.
Alysanne rides graceful Silverwing, often coiled together witgh Vermithor.
...and your own mother Rhaena, Jaehaerys' oldest sibling, rides Dreamfyre.
Of course, you are not on best terms with your mother, either. In fact, you may resent her more for taking you from King's Landing than you resent Jaehaerys for stealing your throne. But she has over the years grown resentful of her rights being skipped over by Jaehaery's revolt against Maegor, too.