The symbiosis between data and models to unveil the mysteries of multiple stellar populations. Still unanswered, the multi-populations phenomenon remains one of the most intriguing open questions of stellar astrophysics. The present-day internal dynamics of multiple stellar populations provides a fundamental window on the physical processes leading to their formation. With this in mind, the advent of precision astrometry, photometry, and spectroscopy (Gaia, Muse, HST, JWST) give us the unprecedented opportunity of studying the internal kinematics of multiple populations over a wide field of view (Cordoni et al. 2019). Furthermore, the coupling of observations and models finally provides us with an unparalleled understanding of the eclectic behavior of multi-populations (Aros et al. 2019). On the other hand, young massive clusters, being the younger counterpart of globular clusters, like infants to grandparents, constitute an amazing chance to look at these mysterious objects from a completely new and unique perspective (Martocchia et al. 2018).