The Friend - The Family Helpers

Single mother Fiona knows that her seven-year old son Eddie has autism, but doesn't know much about it and how it affects him, so doesn't know how she can help him. Then Tom appears at the door saying he has come to help them find out about autism and make their life easier. He helps Eddie tell Fiona how autism affects him and how she can help, then helps Fiona by letting her know what autism is all about.
This brings Fiona and Eddie closer. But who is Tom? How comes he just appears and disappears? How comes he knows about autism?