These statues are placed in Zojoji temple (Minato-ward Tokyo). They are the statues of Zizo. Zizo is one of the most popular Boddhisattva in Japan.
Zizo is usually the guardian deity of kids, travelors and pregnant women. The statues of Zizo in the picture above are especially dedicated to babies who died before or soon after the birth. So they look like babies and wear bibs. Colorful pinwheels were traditionally used to entertain babies in Japan. People who have lost their babies in various reasons worship this Boddhisattva.