Are there any problems with using fish oil supplements in children with autism?

Give it a try: The problem is getting them to actually take it! :-) if you can actually get the kid to ingest it, i recommend a trial of fish oil for most with autism. Although more research is needed, some research suggests modest benefits from fish oil, and no evidence of any harm. In general, fish oil and a multivitamin (+/- iron depending on constipation) are a good idea for most kids with autism.

Fish oil: There is usually no problem, and it may help. The one problem is that families may ignore more proven treatments. So try fish oil but do not ignore counseling, special education, group counseling, and psychiatric medication.

Mercury: This depends on the source of your fish oil, and if there was significant buildup of mercury in the fish that was utilized to manufacture the fish oil. Here is a good study from Mass general on the subject. Stay away from anything with "Jennie McCarthy" on it. Of note, placebo effect in place for these small studies. http://www.massgeneral.org/children/services/lurie-center/Omega-3.aspx

No: should not be any problem using fish oil supplements.