This blue liquid is basically a gel called the polymer. It can easily be bought from a garden store and is often showed being poured onto a diaper for fun. It is super absorbent. It is a gel used during the time of gardening. You can sprinkle it onto the flowers. It is convenient and can be perfectly used in the dry climate where the plants require watering atleast twice a day.
This liquid can easily be absorbed by the diaper as shown in the pictures and forms crystals inside the diaper. The reason why this is shown so often is that the babies often make the cloth wet but in diapers they will not be able to wet it so easily because of their super absorbent quality. The liquid turns into gel and is absorbed by the diaper as soon as the baby wets the diaper. Turning this liquid into gel. This is the meaning of pouring blue liquid in the diaper. They also start looking like ice cubes once poured in the diapers. This is also acrylic polymer which is not very safe in the soil.