<p>Stars are born in darkness, deep within cold, dense molecular clouds where gravity drives the collapse of gas and dust, which gives rise to protostars, the earliest stages of stellar evolution. Once considered purely thermal sources, these young systems are now emerging as sites of energetic non-thermal activity. Although radio synchrotron jets hint at the presence of relativistic electrons, direct confirmation of proton acceleration has remained elusive. Here we report a statistically significant detection of γ-rays from a population of young stellar objects, thus revealing a Galactic class of Gamma-Loud Protostars. Observations point towards particle acceleration within protostellar jets, where γ-ray emission arises from protons interacting with surrounding molecular clouds via pion decay. We find a correlation between cosmic-ray output and bolometric luminosity, which indicates that particle acceleration scales with the mechanical power of the system. These findings open a new observational window into the role of non-thermal processes in protostellar evolution and indicate that γ-ray studies of protostars could provide critical insights into accretion, ejection and feedback in star formation. This previously overlooked emission traces the energetic feedback that young stars inject into their surroundings, which shapes the conditions for subsequent star and planet formation.</p>