What is being described is a travel transition failure, and yes they are very common. It's not just WA where these happen, any kind of travel (Uni World, Oasis Landing, custom destination travel with mods) can produce these.
If not averse to using mods, NRaas Traveler (together with Overwatch and ErrorTrap) works very hard to prevent these from happening.
Without mods, all we can do is relieve as much stress on the game as possible, try again, hope for the best and hope they don't get stuck in the vacation world later unable to transition back home (be sure to have at least a couple of saves to revert to regardless).
-- Do not be logged in at the Launcher or in-game levels before travel
-- Turn ALL of the graphics options down the their bare ugly minimums and switch off the checkbox for Advance Rendering (this will all look horrible, but they can be set back again after a safe arrival)
-- Attempt travel only after having freshly started up the game from the desktop or Origin, which you would have to do after altering those graphics settings anyway
Or all of those plus the mods would usually be sufficient to get them through. If all else fails, there might be something wrong with the instance of Champs les Sims (France) in this one ongoing game even if it has never been played in before, but we can fix that if need be if none of the above helps.
