We knew about Kevin's middle-school-aged son since we saw him as the family gathered for Rebecca, and as of season five, we know his name: Nicholas!
Kevin's daughter was a surprise from the season four finale, since Madison revealed she was pregnant with twins. Her name is Frances.
We saw Kevin rediscover a sketch his dad had made of the house he wanted to build, and now we know he had that house built on the hill next to the family cabin.
By the time this family gathering takes place 12 years after the birthday party at the cabin, Kevin and Randall have apparently mended their rift. We saw them work through their issues in season five, so it's nice to see that they can still be in the same room together.
Despite some questions about whether Randall and Beth's marriage might make it, they're still happily together in the future, which is good to know.
He says when he arrives at Kevin's house that he talked to Jack, and "they're on their way." We assume that "they" includes Kate, but we don't know, since there's no mention of her. Kate is one of the few who has not yet appeared in this future story yet (along with Miguel).
Nicky plays a significant role in the family by the time they all gather in Kevin's house in the future. He's sitting by Rebecca's bedside, and Randall asked about him when he arrived at the house. He is also wearing a wedding ring.
By 12 years in the future, Rebecca's health seems to have deteriorated. Randall has to reintroduce himself when he visits her.
This is what Kevin looks like in the future. That's all.
Kate and Toby's son Jack grows up to be a successful singer. In the latest flashforward, he and his wife Lucy have just had a new baby named Hope.
The season four finale revealed that Kate and Toby were adopting a daughter, revealed to be played in the future by Adelaide Kane. Her name is Hailey, she works at an art gallery, and she dropped everything to be there to visit her brother's new baby in the hospital.
The season five episode "The Ride" finally introduced adult Deja (La Trice Harper) and adult Annie (Iyana Hailey) and brought all of Randall and Beth's daughters together for the first time in the future. We learned that at the time of this gathering around Rebecca's bedside, Deja is studying to be a doctor and is secretly pregnant, and she and Annie are close enough for Annie to be one of the few who knows. Annie also seems to know a lot about babies!