Magnetic fields play a significant role throughout the life of low-mass stars¹⁾; for instance, they are very efficient at spinning down Sun-like stars by dissipating their angular momentum through magnetic braking, via mass loss from magnetically-driven winds. Magnetic fields have the largest impact in early phases of evolution, when stars and their planets form from collapsing parsec-sized molecular clouds, progressively flattening into large-scale magnetized accretion discs and finally settling as pre-main- sequence (PMS) stars surrounded by protoplanetary discs. At an age of 1-10 Myr, low-mass PMS stars have emerged from their dust cocoons and are still in a phase of gravitational contraction towards the main sequence (MS). They are either classical T-Tauri stars (cTTSs) when still surrounded by a massive (presumably planet-forming) accretion disc or weak-line T-Tauri stars (wTTSs) when their disc has mostly dissipated. TTSs have been the subject of intense scrutiny at all wavelengths in recent decades given their interest for benchmarking the scenarios currently invoked to explain low-mass star and planet formations²⁾.