I personally would have an ad up at the local university for a generic part-time nanny position, and then when you speak to them personally explain that you'd like them to do some educational activities with your child during that time. See if they are open to that, then, once you've met with them, you can get further into where your son is at and what he needs. I think nearly any college student would have the knowledge necessary to work with your son, the important part is finding someone who loves children, has patience and wants to have fun and entertain your son. He might not always want to do "learning" with this person, and it would be good to have someone who's also okay taking him to the park or the zoo, or whatever.