The ground state vibrational energy levels of jet-cooled H2CSi and D2CSi have been studied by a combination of wavelength-resolved fluorescence and stimulated emission pumping (SEP) techniques. By taking advantage of the vibrational selection rules and Franck-Condon factors and selectively pumping upper state single vibronic levels, readily assignable low-resolution emission spectra were obtained. Higher resolution SEP spectra were recorded to give precise measurements of the vibrational band origins of many of the lower-lying vibrational levels. All of the vibrational frequencies, except for the Franck-Condon inactive CH asymmetric stretching mode, nu (5), have been determined for both isotopomers. The CH2 rocking mode (nu (6)) is found to have a very low 263 cm(-1) frequency in the ground state. The spectra are complicated by unexpected activity in the out-of-plane bending vibration.