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The newborn planetary system comprising of four gas giants transiting the bright 23 Myr old star V1298 Tau presents an exciting opportunity to probe the atmospheric properties of planetary systems immediately post-formation comma and to do so within one system. We propose to observe a transit of the hottest gas giant in the system comma V1298 Tau c comma using the HST-WFC3-G141 grism comma to measure the strength of water absorption features. The NIR transmission spectrum of this hot Neptune planet will be used to constrain its metallicity and cloud or haze coverage comma which in turns will inform planet formation and evolution models. In conjunction with the previous WFC3-G141 observations of the warm gas giant V1298 Tau b in the system comma our observations will enable comparative exoplanetology of planets within a multiplanet system fresh after formation. When put in the context of directly imaged planets at wider orbital separations but similar age as the V1298 Tau system comma the inferences from our comparative study of a close-in multiplanet system will put constraints on the effect of insolation and location in the planet-forming disks on the bulk planetary composition and properties.