we all should know sign language

Yesterday, I along with some of my friends were visiting Bilaspur JJ Camp (slum), Badarpur, Delhi and interacting with children and parents. During this visit, we met two children who were suffering from hearing impairment. They were knowing sing language but we were not. Result was: there was no effective communication between them and us. What is wrong if we all learn sign language? This question came to my mind when I found myself helpless in interacting with these charming children.