In this article, resonant and high-energy X-ray diffraction studies together with magnetization and transport measurements on lightly doped manganites will be presented. The main focus is put on the metal-insulator transition in La1-xSrxMnO3 with 0.10<x<0.15 and, in particular, on the stabilization of the ferromagnetic insulating (FMI) phase of these compounds. The experimental results reveal an orbital rearrangement at the metal-insulator transition which is tightly connected to the magnetic degrees of freedom. More precisely, the double exchange mechanism is found to be essential for the stabilization of the FMI phase. This conclusion is further supported by the studies on (La1-yPry)7/8Sr1/8MnO3 and the layered compound La7/8Sr9/8MnO4.