I asked the girls what they were playing on the iPads. Turns out it was virtual Hide'n'Seek within the game Minecraft. First they built a huge mansion and then one player looks away from their screen while the other players hide.
I'm all for virtual games, there's very little tidying up to do afterwards!
See here an article about Minecraft classes being put on the school curriculum in Sweden for its educational value:
Minecraft put on Swedish school curriculum.
Also here a link to a brief explanation of the Minecraft game: