We present Raman scattering studies of the structural and magnetic phases that accompany temperature- and field-dependent melting of charge- and orbital-order (COO) in La0.5Ca0.5MnO3 and La0.25Pr0.375Ca0.375MnO3. Our results show that thermal and field-induced COO melting in La0.5Ca0.5MnO3 exhibits three stages in a heterogeneous melting process: At low temperatures and fields we observe a long-range, strongly Jahn-Teller (JT) distorted-COO phase; at intermediate temperatures and/or fields, we find a coexistence regime comprising both strongly JT distorted-COO and weakly JT distorted/ferromagnetic metal (FMM) phases; and at high temperatures and/or high fields, we observe a weakly JT distorted homogeneous paramagnetic (PM) or ferromagnetic (FM) phase. In the high field-high temperature regime of La0.5Ca0.5MnO3 and La0.25Pr0.375Ca0.375MnO3, we identify a clear structural change to a weakly JT distorted phase that is associated with either a Imma or Pnma structure. We are able to provide a complete structural phase diagram of La0.5Ca0.5MnO3 for the temperature and field ranges 6≤≤170K and 0≤≤9T. Significantly, we provide evidence that the field-induced melting transition of La0.5Ca0.5MnO3 is first-order, and resembles a crystallization transition of an “electronic solid.” We also investigate thermal and field-induced melting in La0.25Pr0.375Ca0.375MnO3 to elucidate the role of disorder in melting of COO. We find that while thermal melting of COO in La0.25Pr0.375Ca0.375MnO3 is quite similar to that in La0.5Ca0.5MnO3, field-induced melting of COO in the two systems is quite different in several respects: The field-induced transition from the COO phase to the weakly JT-distorted-FM phase in La0.25Pr0.375Ca0.375MnO3 is very abrupt, and occurs at significantly lower fields (∼2T at ∼0K) than in La0.5Ca0.5MnO3 (∼30T at =0K); the intermediate coexistence regime is much narrower in La0.25Pr0.375Ca0.375MnO3 than in La0.5Ca0.5MnO3; and the critical field increases with increasing temperature in La0.25Pr0.375Ca0.375MnO3, in contrast to the decrease in observed with increasing temperature in La0.5Ca0.5MnO3. To explain these differences, we propose that field-induced melting of COO in La0.25Pr0.375Ca0.375MnO3 is best described as the field-induced percolation of FM domains, and we suggest that Griffiths phase physics may be an appropriate theoretical model for describing the unusual temperature- and field-dependent transitions observed in La0.25Pr0.375Ca0.375MnO3.