I need to get back into the swing of things, and this sounds like the perfect roleplay idea to do so.
I do agree with Crow, depending on the world. If it's a fantasy world with magical beasts and races it would be a bit more interesting if they were either reincarnated as, or plopped into the bodies of various peoples. It would allow for more creativity with the characters, and if you chose to plop them into the bodies of fully grown people, it would still have the overall feel of getting used to a new world, with the added bonus of getting used to a new body as well.
If it's more of a low-fantasy setting, without elves and dwarves and such, it would actually make more sense to just plop the modern characters into the world, would be rather humorous seeing them panic about their phones not working while the locals are panicking that strange wizards are trying to destroy everything with a malfunctioning magical glowing tablet.