Hijuelos are the baby agave shoots or “pups” that grow up around the main plant when the plant has matured to about the 3 years of age.
In the wild agaves reproduce with the help of bats who pollinate the large yellow flower that emerges at five to seven years. As a practical matter this method of reharvesting has been widely abandoned because it takes too long and importantly the stock and flower rob the plant of vital starches required for making quality Tequila.
As such, most farms cultivate the hijuelos and replant them as a means of replenishing the crop. To find out more about Tequila harvesting check out this site.