I've always said that the people of the Trueniverse - that is, you and I who watch TV in the real world - all have doppelgangers in the TV Universe.
And some of us have counterparts in the alternate TV dimensions.
The Toobworld that is now designated as Zombie Toobworld, as seen in 'The Walking Dead' and 'Dead Set', would also be a dimension in which real world people could be found. And that includes kids, like Christopher here.
I have no clue what his televersion from the main Toobworld is up to, but knowing his Dad, it's probably some kind of mischief!