I do not know about resourse materials but, I would suggest being very sure there is a problem before concerning yourself too much. When my son was about 2 his pediatrician told me he was delayed and we needed therapy and such. We had all the evaluations and I took him for therapy and I worried. Turns out he was simply delayed, nothing was wrong. He is in college now in an honors program. It was after the fact that my father said he was a late talker also. It does run in families. I am only saying you MAY not have reason to be concerned.