I would second @lmosenko 's suggestion that you look at SmartTiles. It’s a very popular customizable dashboard which was initially created by a community member who had two kids who thought it was funny to turn off the lights in the other one’s room.
Then they don’t need to have the official Smart things mobile app. And as was also suggested, if you want presence Detection for them you can either give them the arrival sensor or you can use IFTTT presence or Life360.
FAQ: The Many Ways of Detecting Presence
So it’s a little more work to set up, but you can definitely accomplish the end goal. It comes up with housemates and landlord/tenant situations as well. It would be nice if the official features had a way to manage this, but at least there are good workarounds. 