Kangaroo care is the slightly goofy name for holding your diaper-only baby on your bare chest for significant amounts of time (e.g., 20 minutes at a time). It promotes parental bonding (what doesn't, right?), but it also helps kids regulate their temperature better/quicker, improve their sleep quality, and grow more quickly. For this reason, hospitals sometimes use it as part of a NICU regimen for preemie babies.
Brigham and Womens FAQ on kangaroo care
Johnson & Johnson Pediatric Institute study of kangaroo care
