Accretion onto the protostar/disk system is at its peak during the embedded protostellar stages. These young disks (Class 0 and I) are thus expected to be more massive and prompt to gravitational instabilities, with implications for forming multiple systems and planets. Resolving the dust distribution in these young disks down to disk scales is crucial to directly constrain the initial conditions for planet formation and the star accretion process. We present multi-wavelength ALMA observations that reveal the dust distribution down to 6 au for single and multiple embedded protostellar systems. In addition, we show spatial variations of the spectral index in these systems, with implications for their physical structure (optical depth, temperature) and the dust accumulation and growth process.