The main aim of the study is to determine whether intramuscular injection of umbilical cord mesenchymal stem cells can improve the ventricular function of children with idiopathic dilated cardiomyopathy(IDCM); Secondary end-points will be: 1)To explore the possible mechanism of the improvement of ventricular function in children with IDCM and 2) to evaluate the safety of intramuscular injection of umbilical cord mesenchymal stem cell.