>>116754542The Future Foundation was a part of the time skip that happened for the F4 as a whole, so Val and Franklin were interacting with kids in a similar age group prior to returning to Earth.
Also keep in mind that the "time skip" was the F4 rebuilding the Marvel multiverse mostly off-screen after the events of Secret Wars, and it was a combination of Franklin's reality-warping/building powers + Molecule Man providing the raw power/energy to let this rebuilding take place.
It was only near the end of said rebuild (ie., when the new F4 title began) that Franklin and Reed noticed his powers were starting to wane, and that was the main reason for returning to Earth: to see if they can save his powers.
