It´s amazing to see lot of chinese members here posting endless bs, nonsense and insult.
First, your country did help VN to help yourself, trying to keep the French, the US away from China. Not so generous than propaganda says everyday to you. "Thank" to China Vietnam was divided after the first Indochina war.
Second, China itself was poor and weak. The really power helping North Vietnam during the second Indochina war was the Soviets. Did you forget the Great Leap Forward and Cultural Revolution with million of deaths? one of the most deadly mass killings of human history.
Third, the real face of China showed in the invasion of Vietnam in 1979.