It is great to have the kids learn some sign language.  It is like learning a 3rd language, except that they don't have to slog over books and grammars and exams.  If you have a child who is taking his time picking up speech, sign language is a great alternative to communication.  It really helps with the frustration level.  When Dominic was little, he was a little slower in picking up words.  I decided to teach him some simple signs and it did help with communication. Don't worry about sign language making speech delay worse.  When the child is ready to pick up speech, he will naturally drop the signing and just verbalise what he wants to communicate.  This was what happened with Dominic.  The best part is that with practice, they actually will remember the signs they learned.