All of the React series have gone over some of the same topics as another React in some form or another at various points, usually because fans are continuously requesting it even after the initial videos.
- Most of the earlier Elders React episodes covered topics that were already covered by Kids and Teens React. They eventually got away from this.
- Kids React has repeated some topics from the other Reacts, as they've discussed about One Direction, which was once a topic on Teens React. Nearly nine months after the kids, the YouTubers reacted to the boy band.
- Kids React also covered Here Comes Honey Boo Boo, which was sort of covered before on Teens React with Toddlers & Tiaras as a subject.
- By the time "Teens React to Bullying (Amanda Todd)" was released, since bullying was already covered by Kids React, all of the first three React series have reused a topic at some point.
- "Gangnam Style" was one of the first three videos shown in YouTubers React, though it was already covered before by Teens and Elders React. Unsurprisingly, the YouTubers were dismayed at the choice of video, as it had long since peaked in popularity and was experiencing major hype backlash by then. Even Shane Dawson went Screw This, I'm Outta Here for a second.
- It gets ridiculous in episode two when the first video on that episode is "Chocolate Rain" (last seen on Kids React), with Tay Zonday himself in the studio.
- Episode four of YouTubers React features Fred, which came up once very early in Kids (twice if you count Lucas Cruikshank showing up in person for Teens).
- If we're going purely by topics, elaborate/extreme pranking has been covered across the first three series:
- "Kids React to Fake Celebrity Prank" and "Rémi Gaillard"
- "Elders React to Scary Elevator Prank"
- "Teens React to Prank vs Prank" and "Improv Everywhere"
- Setting a new record for how quickly a popular topic can be repeated,note the "Harlem Shake" got covered by the teens a week after the kids covered it. Apparently, fans needed to know both age groups' opinions on it very badly. It seemed like after the Teens React episode it was pretty much inevitable that they would also get the elders and YouTubers reacting to it as soon as possible, but thanks to the rapid burnout the meme suffered this topic never got to be covered on the other two shows.
- A similar thing happened with "The Fox". It was first an Elders React video around the time it was starting to take off. Shortly afterwards, the video became massively popular worldwide. Since the more popular viral videos have, more often than not, been shown in Teens React episodes, it was only a matter of time before it was their turn. Two weeks later, the inevitable happened.
- And speaking of "The Fox," the 2013 YouTube Rewind video went to the Teens first and then the YouTubers. Only the YouTubers got the 2012 video.
- A similar thing happened with "The Fox". It was first an Elders React video around the time it was starting to take off. Shortly afterwards, the video became massively popular worldwide. Since the more popular viral videos have, more often than not, been shown in Teens React episodes, it was only a matter of time before it was their turn. Two weeks later, the inevitable happened.
- Boxxy was shown in Teens React and YouTubers React.
- On the other hand, it took them one and a half years to revisit Hatsune Miku for Elders React (now with an additional clip with Kagamine Rin and Len).
- The Japanese dog commercial was shown on Kids React and YouTubers React.
- "Teens React to the Cup Game" could be considered a Bowdlerization of "YouTubers React to the Knife Game".
- Don't Hug Me I'm Scared was shown to the kids a couple months after the YouTubers.
- "Teens React to Happy Wheels" is a two-for-one deal, calling back to PewDiePie playing Happy Wheels in one past Teens React episode, and the teens themselves actually playing in another one (and this time they were a bit more enthusiastic, and not without reason).
- PewDiePie himself was featured again in a much later Elders React episode.
- Arguably the first time they did this in the same series is "Kids React to Lily's Disneyland Surprise...AGAIN!" Some of the kids in that episode were also in the episode "Kids React to Lily's Disneyland Surprise", and those kids knew that something seemed familiar when they were watching the former video.
- How about Rebecca Black? She manages to have three different music videos for React topics (two for Kids React ("Friday" and "My Moment"), and one for YouTubers ("Saturday"), which includes Rebecca herself in the YouTubers one).
- In Fine Time episode 18
(which was published on February 22, 2014, a couple days after "Elders React to Flappy Bird") the Fine Bros revealed that a Teens React episode on the hit mobile game has already been recorded since many React fans have been wanting to see the teens' reactions to it. All the Fine Bros were waiting for now is to see if the fans still want to see it or not, though it would be a while before it was published. While several comments made about the announcement were very positive towards it, there were more than a few comments from those who are exasperated about the Flappy fad. Those fans said that the Elders React episode is good enough and the teens, who unlike the elders would have probably already played it before, should react to something else. Nevertheless, the Teens React episode was eventually published on April 6, 2014. - It's already happened now on the React channel as the teens played Happy Wheels again.
- This has now been played completely straight with a second "YouTubers React to K-pop" video in August 2014.
- And again with a third one in September 2015.
- And again with a fourth in March 2016.
- And again with a fifth in August 2016.
- "YouTubers React to Darude - Sandstorm". No, it's not because it's covering another EDM song. It's because the Fine Bros Rickrolled the YouTubers again.
- Donald Trump was covered four times, first by the kids, then by the teens (for the Access Hollywood scandal), then a generations-wide election episode, and finally the teens again for a Dutch parody video. Far more serious Trump-related content was covered over the summer, with college kids reacting to Charlottesville and the teens once more for the repeal of DACA.
- The ComUp (short for Community Update) is essentially Fine Time with the Community Team, and they've stated as such on the show itself.
- There have been two episodes on online crane game Toreba, with the first taking place in the studio and the second taking place in Japan.
- There have been two "Try Not To Eat" challenges based on Food Wars!, each done for the premiere of a specific season, and there have been three Disney versions of the same challenge.
- Not counting her songs being included in the "Do They Know?" challenges, Avril Lavigne has been covered by the channel twice. First was her infamous "Hello Kitty" music video in a 2014 Kids episode, then her entire career in a 2019 Teens episode which even features half of the kids who reacted to her previously.
