> You don't need a house. Many of the kids I knew growing up lived in apartments.
Apartments are part of the housing market
> If they lived in a house they could inherit it from their parents.
Teenagers probably want to move out of their parents home (be it a house or apartment).
> Why is the housing market something children worry about?
See above : teenagers often want and look forward to independence, and housing is 100% central to that goal. Their future horizon may be a little shallower than that of the average adult, but they do have a horizon - i.e short term goals that they want to achieve.
At least for me, that meant figuring out how I was going to actually live on my own come 18. You can bet I was worried about housing prices (even if my immediate goal was to rent).