  Space observatories have provided unprecedented depictions of the many
variability behaviors typical of low-mass, young stars. However, those studies
have so far largely omitted more massive objects ($\sim$2 $M_\odot$ to 4-5
$M_\odot$), and were limited by the absence of simultaneous, multi-wavelength
information. We present a new study of young star variability in the $\sim$1-2
Myr-old, massive Lagoon Nebula region. Our sample encompasses 278 young, late-B
to K-type stars, monitored with Kepler/K2. Auxiliary $u,g,r,i,H\alpha$ time
series photometry, simultaneous with K2, was acquired at the Paranal
Observatory. We employed this comprehensive dataset and archival infrared
photometry to determine individual stellar parameters, assess the presence of
circumstellar disks, and tie the variability behaviors to inner disk dynamics.
We found significant mass-dependent trends in variability properties, with B/A
stars displaying substantially reduced levels of variability compared to G/K
stars for any light curve morphology. These properties suggest different
magnetic field structures at the surface of early-type and later-type stars. We
also detected a dearth of some disk-driven variability behaviors, particularly
dippers, among stars earlier than G. This indicates that their higher surface
temperatures and more chaotic magnetic fields prevent the formation and
survival of inner disk dust structures co-rotating with the star. Finally, we
examined the characteristic variability timescales within each light curve, and
determined that the day-to-week timescales are predominant over the K2 time
series. These reflect distinct processes and locations in the inner disk
environment, from intense accretion triggered by instabilities in the innermost
disk regions, to variable accretion efficiency in the outer magnetosphere.
