I know several children with varying degrees of autism. The autism spectrum is so broad and encompasses so many other disorders that it is hard to say what you will come across. Being that it is mild autism, it may not be overly evident that the child even has autism.
I would have no problems meeting with the mom and child to see if they fit into my program. I would just make sure the mom gives me detailed descriptions on his routine, his interests, what may or may not upset him, how to calm him when/if he gets upset, etc...

Good luck and I hope everything works out for you.