When considering the efficacy of antipsychotic interventions in the paediatric population, there tends to be an increased level of unique intra-individual  factors involved - due to to the developmental dynamics that are present throughout childhood and adolescence. 

While there are  commonalities in the symptoms that both risperidone and aripiprazole have been found to alleviate, the differences in the levels of associated adverse effects may carry as much significance as efficacy when being considered for use with individual children and young people.  With reference to this, I have attached a recent Agency for Healthcare Research and Quality (AHRQ) presentation on "First- and Second-Generation Antipsychotics for Children and Young Adults". 

I hope this response is of some functional assistance.

The case studies available are few and relate to a small number of patients. Therefore, it is difficult to assess the therapeutic response to these two antipsychotics. In our limited experience Aripiprazole appears to be better than risperidone. Design and conduct a comparative trial between aripiprazole and risperidone is difficult because you have to identify the most important outcomes to evaluate. Obviously, the outcome affects the risk / benefit ratio of the drug. The effectiveness of the drug is also conditioned by the non-drug therapies and the context of the patient's life. Furthermore, the use of antipsychotics as antidepressants is an empirical choice, based on the principle "ex adiuvantibus" and not on clear scientific evidence.

There are no drugs "for autism spectrum disorders." Risperdone received FDA approval for use regarding "agitation" in people with an ASD diagnosis (based on a very short and small study, as you probably know) but given the high side-effect profile and long-term health impact of this drug, particularly where children are concerned, it really is not a very useful option. In the UK, the National Institute for Health and Care Excellence (NICE), which works to produce best practice guidance for treatment across the NHS, has produced very clear and unequivocal guidelines regarding medication and ASD: http://www.nice.org.uk/guidance/QS51/chapter/Quality-statement-6-Treating-the-core-features-of-autism-medication

It makes more sense to investigate and address the cause of the "agitation." Those of us working directly with children and adults on the spectrum generally find that the answer can be found in changing the environment, as much agitation derives from sensory overload. It's also important to train staff and parents/carers well, so that they can adapt communication and create consistent structure in tasks and expectations. After sensory-perceptual difficulties, problems arising from difficulty with communication or executive function are the most likely causes of agitation. It should be fairly obvious that none of the factors discussed in this paragraph are treatable with medication--therefore if medication is being used, it is ikely being used improperly and unethicall, e.g. as a "chemical cosh."

There is somewhat more research backing for the use of medications, such as SSRIs, by people with autism who also experience severe anxiety or depression and request help with these additional conditions. That said, while medication may be useful in these cases in treating acute symptoms, they are not a long-term fix and may carry with them additional risks such as lowering the seizure threshold--a significant problem in a population with a high risk for seizure disorders. So when medication is used for anxiety or depression by people with ASD, it should be as the initial part of an overall treatment plan that includes non-medication strategies keyed specifically to the autistic cognitive profile.

Risperdone and Aripiprazole are FDA approved drugs for irritability and aggression in children with Autism . We need to keep in mind that medication always augments the non-pharmacological interventions. Both drugs can cause adverse effects .