Nuria2012-
I am not sure what country you are writing from, and sign language does differ from country to country. If you are wanting to teach sign language as it is used in Hard of Hearing and Deaf cultures, you will want to make sure that you stay away from the 'baby' signing that is more of a system of sign language adapted for babies to make the signs simpler.
For example, I am in the USA and we use American Sign Language-I did this (and still do!) with my hearing daughter and it has been amazingly rewarding and beneficial.
Take a look at
http://www.signingtime.com/Hope his helps!
Btw-there are lots of parents of hearing toddlers in this forum using sign language with their! I have never actually heard of a parent who regretted it, even if their children gave it up when starting to speak. To be
able to really communicate with your child before they can speak? It really is a priceless gift
If you have an IPhone or IPad, take a look at the Signing Time ASL app ( the $4.99 version has sign videos and signing songs taken directly from the DVDs-like Leah's Farm, always a favorite!)