Harley is seven, and he and Elspeth are hanging out in the Québec capital (because the rest of the Golden Coven is doing so), and as is usual in capitals with major wolf villages, she, he, and Jacob stay in village quarters during this time.
The capital as a whole moves less often than it once did, now that people can readily teleport to other sites to handle things there; this is the first time in Harley's life that they've been to Québec for anything other than a brief visit, so it's the first time he's seen the Imperial Alpha house in which Jacob, his imprint, and her fosterling are entitled to live.
They have neighbors. One of these is a seven-year-old puppy boy, who is currently making a snowfort.
[No one understands why alts happen, at least not yet, but your alts are versions of your personality and basic traits - and, in most cases, appearance - from other worlds and circumstances.]
"Alts are people from different worlds who are like the same person!" says Harley, approximating this explanation as best he can without copying it verbatim.
"So the imperial something is from another world but he's - like you sort of?" fumbles Zeus. "But what if you grow up to be different? He's a grownup, you could be anything you wanted when you grow up, right?"
"I can be anything I wanna be when I grow up, but I'm still gonna be me," he says. "And I'll be one of the Jokers. There's lots and they're all the same but different and I'm gonna get to meet them when I grow up!"
"Because grown-up Jokers have sex with each other and it'd be weird when I grow up if I knew them all now!" he says, secure in the knowledge that this is an Elsie-splanation and is therefore absolutely true.