The Baby Eruptodon has the same appearance and coloration as his mother.
The baby was born after its egg hatched at the sacred hatching ground and the Defenders of the Wing took care of him for a few weeks. After the battle against Ryker Grimborn and the Shellfire, Mala felt that the baby was not safe on their island. So, she gave it to Fishlegs Ingerman so that he could help take care of it and keep it safe. Thus he took it along with him back to Dragon's Edge.
When Ryker later attacked the Edge, Fishlegs took it to safety. Noticing the volcano "waking up" from the blasts, he took the Eruptodon up to the volcano's mouth. The baby ate the flow of lava and has seemingly saved the Edge.
The baby was first seen as as egg in "Out of the Frying Pan", after being laid by its aging mother. Unable to find the strength to carry the egg to the ceremonial site inside the volcano, Hiccup, Fishlegs, and Mala take on the task of getting it to the life giving lava before the egg petrifies and dies. Werth the help of Fire Terrors, the egg reaches its ceremonial site just in time, and is seen with a heartbeat inside as the lava enfolds it.
A few weeks after hatching, the baby is seen with its mother in "Shell Shocked, Part 1", eating the lava from their home volcano. With the attack from the Shellfire, Mala asks Fishlegs to take the young dragon somewhere safe. So he takes it with him back to Dragon's Edge.
But when the Edge is also attacked in "Shell Shocked, Part 2", Hiccup instructs Fishlegs to take the baby to the center of the island, thinking it would be the safest place from the Shellfire. But the local volcano starts waking up with the Shellfire blasts, threatening their safety again. So Fishlegs has the baby eat the lava, while Meatlug guards it, and Fishlegs guards Meatlug.
In "A Matter of Perspective", its mother is old and slow moving, and unable to reach the village in time to save some of the houses from the overflowing lava. So the baby, now much bigger, is beginning to take over. The two dragons exchange an understanding that it's time for the roles to be passed on to the next generation and the older one to retire to Vanaheim. With that, the Baby Eruptodon takes over as the new Great Protector for the Defenders of the Wing.