The low field susceptibility versus temperature has been studied for the series of colossal magnetoresistive (CMR) manganites Ln0.7Ca0.3-xSrxMnO3 (Ln = Pr, x = 0.10, 0.05, 0; Ln = Nd, x = 0). The effect of the average size of the interpolated cation upon Tc is confirmed for the larger sizes (Ln = Pr, x = 0.10, 0.05) showing a classical ferromagnetic behavior at low temperature in agreement with the neutron diffraction studies. For a smaller size of the A-site cation (Ln = Pr or Nd, x = 0) an original behavior is observed: the χ′(T) curves show a spin-glass-like behavior with a cusp at Tcusp, whereas the neutron diffraction data in zero magnetic field evidence a ferromagnetic component starting around Tcusp.