I don’t believe the child came to Tokyo alone.
Ung seems to only be classed as an Adjective everywhere I have looked and using it as a Noun (ungEN) is not something I can pin down.
Is this quite a common way of saying “the kid”, please?
ung is the adjective,
unge is the noun.
unge (common gender)
Doh! Gone back to my Prismas and, of course, Unge came after Ungdom - on the next page. Must scan up and down more. 
Thank you
It should be noted that unge can have a negative connotation, hence the saying “egna barn och andras ungar”.
In what context would you use that one? I’m not a fan of kids so may need it one day
It’s about how parents think their own kids are always saints, compared to other, naughty children.