We propose to collect deep near-infrared (NIR) images of two peculiar Galactic globular clusters (GGCs), NGC1851 and M22, to explore the properties of their multiple stellar populations. These GGCs display multiple sequences along the red-giant and sub-giant branches in ultraviolet-optical color-magnitude diagrams (CMDs), and spectroscopy confirmed they host multiple stellar populations with different light- and heavy-element abundances and total content of CNO. How these populations originated is still a mystery. We plan to solve this puzzle by using NIR photometry of low-mass main-sequence (MS) stars: these are brighter in the NIR regime, and the lower part of the MS is more sensitive to heavy and light-element abundances in NIR compared to optical colors. We plan to compare the observed NIR CMDs to theoretical models that include new bolometric corrections taking into account different chemical patterns to characterize the chemical composition and population ratio of the different sub-populations in the GGCs. The presence of chemical inhomogeneities in MS stars similar to those found in the giant stars through spectroscopy will confirm their primordial origin. Furthermore, we will derive the mass function of each stellar sub-population and investigate for the presence of differences. The new NIR data will be combined with archival HST data to derive accurate proper motions for MS stars and to characterize the kinematical properties of the different sub-populations. This analysis will shed light on the origin of multiple populations in these very peculiar GGCs. This work is preparatory for studies with JWST that will allow us to apply the same technique to farther GGCs.