My step son is having trouble with his speech, What should we do about it?

I am sure this is occuring becuase he has not had any one teaching him and he should of started school but his mother is a fool so she cares less about what happens to him, he does not live with her and she gave him away to a friend of hers a couple years back when my husband was incarcerated for child support when we have him with us its like he is active but he does not know how to do much and his speech is horrible I want to help him but I feel I can't do anything about it by the way he is 5 years old going on 6 at the level of a 2 year old child