The black kid gazing longingly at a trumpet in a shop window is apparently a well-known motif to Japanese people of a certain generation. The most commonly-cited origin is this JACCS credit card commercial: http://www.youtube.com/watch?v=-cyQICd5lyo but it spawned many references and parodies (and itself may have been inspired by stories of Louis Armstrong and/or other jazz musicians).
My first impulse was to translate it as "like a fat kid looks at cake," but it doesn't quite fit, and Ayazou continues the reference in the next page, so I left it as-is.
However, a new problem has cropped up. While I'm at work, it seems she gets really lonely being at home all by herself. Every day when I come home, she looks at me like a black kid yearning for a trumpet.*
*Seriously, that's what it says. It's a pop-culture reference to a 1980s(?) Japanese credit-card commercial.I feel sorry for her. Yukkuris have a natural tendency to dislike being alone. But what should I do?"Hmmm..."Yuuu yuuu