It's Friday evening in Shibuya. The sun is setting, the neon is flashing and the crowds are swelling. And so with beginning-of-the-weekend fever in the air, it is perhaps little surprise that Madonna is already blaring in one karaoke room on the second floor of a building near the station.

It may not yet be 7 p.m., but three revelers in particular are having a ball: one is shaking a tambourine, another is frantically pressing buttons on the track machine and a third is standing on the fake red-leather banquettes waving his arms in the air.

So far, so Friday night. Apart from one critical detail. These three enthusiastic karaoke singers are not students, salarymen or housewives. Nor are they inebriated as a result of the temptingly cheap all-you-can-drink offer. They are, in fact, babies.