By this age your child must weigh atleast 13 to 14 kg and must grow to a height of atleast 3 feet.  But growth rate is variable from child to child and it can be influenced by hereditary,  nutritional as well as health related conditions. Respiratory tract troubles like tonsillitis, adenoid growths are the most common causes for less growth in many children. But other causes must also be eliminated.  Consult a nearby pediatrician or a homoeopathic physician once to know weather your childs decreased growth rate is due to any disease condition or by simple lack of nutrition.