In a nutshell, the elf's job is to head back to the North Pole every night and report the day's happenings to Santa. More specifically, were the kids naughty or nice? The next morning the elf returns and positions himself in a new location for the kids to find....One critical rule is that they must never touch him or he'll lose his power.
So far, the triplets are playing along. Alec takes "Clark" a bit more seriously than Julia and Vivi, but they all like getting up and searching for him. I don't believe the creators had multiples, but it's an interesting experiment...more to follow.