To the best of my knowledge (and I've looked) there is not a single scientific long-term randomized study showing the effectiveness of any type of treatment for autism. This means that when deciding on the best way to help the kid you are going to have to rely on the judgment and intuition of family, friends and special needs specialists. Besides the normal biases the huge problem with doing this is that as an autistic child gets older you would expect him, in an absolute sense, to make improvements in many metrics (just as typical kids do) even if whatever special stuff was being done for him had absolutely no impact on his condition. Another problem is that, based on my observations at least, the women who devote their careers to the needs of "special children" tend to be of the very happy/uplifting/optimistic types which undoubtedly causes them to have a more positive assessment of treatment than should be justified and this bias outlook negatively impacts the research that makes use of the subjective judgments of autistic professionals.

Rather than spending time reading about autism you can probably better help this child by playing with him and doing stuff for his parents so they have more time to play with him, although ignore this advice if you enjoy reading about autism and so your doing so isn't a cost.