Fallind down from sofa

When I was washing the dishes in the kitchen. I heard a "kok" sound and found that Hong Zheng was landing on the floor near to the sofa, crying. His dad shouted "oh my goodness"! What happened? Hong Zheng fall down from the sofa. How can this happen since he is already very firm and steady in climbing up and down the sofa? I asked his dad who just sat next to him at his computer but he had no idea either. Hong Zheng was crying very loudly and i quickly approached him and hug him. I was very very sad and i started to cry too. When Hong Zheng saw me crying, he stopped crying immediately and kissing me non-stop. I was so touched of his move. I remembered i told him when he pain and hurt, mommy will feel pain and hurt too. I knew he just did not want to see me sad. I love my son.