Composite scintillators based on grains of cerium-doped gadolinium silicate or gadolinium pyrosilicate crystals are studied as thermal neutron detectors. In these scintillators the grains of the single crystal are fixed by a small amount of non-luminescent gel. In contrast to single crystals, there is no technological limitation with composite scintillators in terms of the size or area of the input window. The very thin scintillation layer (one layer of grains with size less than 0.1 mm) in the composite scintillator is enough to detect thermal neutrons with an efficiency of about 20%. In such cases the scintillation signal is mainly recorded in the peak from 33 keV conversion electrons generated in Gd by thermal neutrons. An efficiency value of about 40-50% can be achieved if the total signal of conversion electrons of 33 keV and of Gd K X-rays of 44 keV is taken into account. In this case a thin composite scintillation layer comprising grains with a size less than 0.5 mm is enough.