I thought your son was in speech therapy? 
Yes a child can learn two languages at the same time, but it can cause delays in both languages. Also, I don't advocate for mixing modalities because it can cause regression when the child has to switch back and forth. Also, I think it is less than advisable to attempt to help a child in homework in a language that is completely different, with different vocabulary, syntax, etc, than that which the teacher will be using to teach, explain and test the child in.
