To lower the calcining and sintering temperatures of 16 at% Y-doped $BaZrO_3$ (BYZ), Gd-doped $BaCeO_3$ (BGC) and Sm-doped $BaCeO_3$ (BSC), nanopowders of $BaCO_3$ and either (i) yttria stabilized zirconia, (ii) $Gd_2O_3$ and $CeO_2$ or (iii) $Sm_2O_3$ and $CeO_2$, were used as starting materials, respectively. BYZ powders were prepared by two mixing methods (i.e. ball milling and magnetic stirring), followed by calcination at $1050-1250^{circ}C$, while BSC and BGC powders were prepared by ball milling and calcined at $1050^{circ}C$. The results reveal that the ball milling and magnetic stirring methods yield similar results for BYZ powder preparation. By adding 1 wt% ZnO nanopowder, the average relative densities of BYZ pellets were increased from ~70% to ~96% at the sintering temperatures of $1300^{circ}C$. Thus, with the utilization of nanopowders and ZnO as a sintering aid, the calcining and sintering temperatures were lowered to $1050^{circ}C$ and $1300^{circ}C$, respectively, while still attaining the relative bulk densities of both BYZ and BGC higher than 95.7%. However, since the relative bulk density of BSC reached only 93% even sintered at $1400^{circ}C$, ZnO was not an effective sintering aid for the BSC fabrication.