Does anyone know of a free downloadable program that changes sketches into 3D icons?

For my job I write children's 4-H manuals, and my boss asked me if i could sketch some horse character icons because the professional they usually get to do it is not responding. I have made some sketches, but now need a program to make them look cartooney. Does anyone know of a program I can download form the internet that will allow me to upload the sketches and make them look like a cartoon?