heres a quick rundown:
The Neutrinos were three kids from Dimension X: Dask, Kala, and Zak. They accidentally transported from Krang and Shredder's teleporter to Earth where they soon after became friends with the Turtles.
Krang however mentioned that the Neutrinos aren't highly thought of in their homeworld. This is later revealed that it is on account that Dimension X is a place of total war and Krang has enslaved many inhabitants of Dimension X. Krang forced people to fight and die for him, which the Neutrinos wanted no part of. Kala cried over the fact that Krang dished out severe punishments for people having fun and enjoying themselves. The Neutrinos were the ones who told the Turtles of Krang, that he was a reptillian warlord who enslaved much of Dimension X until a rebel movement captured and banished him from the dimension, resulting in the loss of his body. Although the Neutrinos are against war, they are not complete pacifists, as their vehicles are equipped with weapons that they will use in self-defense. Although in one episode, Dask said the weapons in the car were apparently required by law in Demension X.
After a brief stunt on Earth, the Turtles managed to become friends with the kids and helped them go back home. The Neutrinos returned a few times afterward, and a romantic relationship between Kala and Michelangelo was implied during those times.
The Neutrinos were apparently a race and the name wasn't just a group name for the three kids. In a later 1987 series episode, Four Turtles and a Baby, it is revealed they are ruled by king Zenter and his wife and child Tribble. Krang tries to blackmail the small people, but eventually the Turtles stop him. A Neutrino baby apparently has powers, but it's unclear if the "grown-up" Neutrinos have powers as well.
The Neutrinos are characters that have been invented for the 1987 animated series.
They appeared in issues #2 and #3 of the Archie Comics, but that story was based on the adventure from the television show. Afterward, the Neutrinos were left out entirely.Three Neutrinos
Although not shown, it is indicated in the first episode of Mutant Turtles: jin Densetsu Hen that the first batch of MutaStones come from the "Neutrino Kingdom".
The Neutrinos can be seen in the background of Chrome Domes stage in the SNES version of Teenage Mutant Ninja Turtles: Tournament Fighters.