I have shared with you all before that there is a little boy that stays at my house during the day. He is now two and was 3 months when I started watching him. At about 4 months I started showing him signs for different words. Including "more" "all done" and "milk". At 9 months he signed "more" for the first time! It made life so much easier when he could share with me before he could talk what he wanted. He learned all sorts of words and still knows it to this day but he uses his words now.
I did the same with little man. He signed "milk" this morning for the first time at 7 months!! I'm so proud of him! Here's a great book on signing. They have videos but I'm not big on babies/kids watching TV. (everyone has their own opinion)
Have you tried teaching your babies sign language?