On the topic of sign language/speech, it doesn't really help or hurt one way or the other. By the time they are old enough to produce any sort of meaningful language (about 12 months), they can learn to speak about as well as they could learn to sign. Any delay in speech caused by teaching to sign is somewhat illusory - It's not a failure to learn, but simply unwillingness to deviate from prior experience. Unless you do something phenomenally, monumentally, unfathomably horrible, kids are absolute language sponges around 2-6 years old and will learn what ever languages they are exposed to on a regular basis.
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The Master said: "It is all in vain! I have never yet seen a man who can perceive his own faults and bring the charge home against himself."
>Analects: Book V, Chaper XXVI
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The Master said: "It is all in vain! I have never yet seen a man who can perceive his own faults and bring the charge home against himself."
>Analects: Book V, Chaper XXVI