I signed with ds and he is now 2 and got fantastic language (puts 5-8 words in a sentence) I started at 6months. He caught on quite quickly but don't expect them to start signing until 12month. We just did the basics eg, Please thankyou, more, water, no more, no, yes, and common objects. once he started he was quite good at it and it takes those frustrating moments out. To encourage them in it, get their little hand and move it with yours in making the sign. Sometimes he did his own little altered version due to his stage of development so don't expect the exact sign from them.

hth