Since we've used Baby Sign Language for Maria, Isabella and no-doubt for John, I'll say a few words about our experience of it here.
Baby signing is a term that's used to teach pre-verbal children to communicate using signs instead of speech. A typical child can say a few words by the age of 1, has a small vocabulary by the age of 2 and can speak intelligibly by the age of 3.
Personally I'd try baby signing as early as 9 months. At that age your baby is probably frustrated when it wants milk, food, a hug, the toilet or a nappy change but has no way of letting you know other than crying.
The Baby Sign Language system uses signs based on the native spoken language and uses the same ordering of hand signs as the spoken language. You'd be expected to speak each word as you sign. This way the sign system mimics the spoken language of the child's family and environment.
Before Maria was formally diagnosed with RTS there was a period from the age of two to three years when I started to think about how to help Maria communicate. Naturally we concentrated on speech but eventually I came across the idea of using signs as a means of expression for Maria. She must have been three years old when I taught her some baby signs and it took her only half an hour to learn about ten signs. These were mostly animal signs since animals always got her excited. Important signs like toilet, milk, more, all gone, where?, book, biscuit, bed, brush teeth, bath, pain, sorry and thank you followed soon after.
Maria was watching everything on the BBC Cbeebies TV channel from the age of one, so she must have watched Something Special. This TV series is designed for children with special needs who are learning Makaton. Thinking about it, maybe she already knew the signs I taught her from watching these programmes. Maybe all that happened when I showed her my signs was to give her 'permission' to use them at home.
When Maria was three years and five months old I bought on Amazon the first of the Sing & Sign DVDs by Sasha Felix. This particular Baby Sign Language system originated from Say it and Sign it (an obscure West Sussex sign system in the UK) but is now compatible with Makaton and Signalong. Maria loved the DVD so much, she almost wore it out by watching it at least a hundred times. Naturally she learnt all the signs and started to use them quite frequently. It soon became her first expressive language, together with babbling (I felt at the time that the babbling probably meant something but I just couldn't figure it out. Looking back, this wasn't very likely since Maria's babbling consisted of just a few different sounds).
Maria is now five years old. To this day Maria uses babbling with spoken English and Makaton signs to express herself. The good news is that spoken English is becoming more prominent and is slowly replacing Makaton. Ask Maria a question nowadays and instead of answering with Makaton, she'll try to say the words in English.
One concern that I had was the fear that learning Baby Sign Language might affect normal language development. Well, in the case of Maria it's impossible to tell but since we taught Isabella to baby sign too then I can only say that there's no discernible effect on her language development; she started to speak as expected. The important thing is that she can understand Maria's signing and even signs for emphasis or for fun.
But the best thing about signing and speech is that our family is now bilingual. Sign language is an extension of our spoken language and has become part of the family culture. Our rare blend of communication modes is one of the things that unites us as a family. We intersect the cultures of the hearing, the Deaf and the disabled to form a new type of multi-cultural community that's barely recognised by the wider public.