Just a quick observation, children with ADHD and Asperger would almost never pass up a good opportunity to talk to any adult. It is (almost to a man) one of the very favorite activities of espeically Asperger youth to talk to adults about all manner of things and love, love, love to interact with them. This is also true of many with ADHD as well, they have great difficulty with peers and are most attracted to younger children and Adults (who will usually listen to them long past thier interest level and are generally way too polite to walk away and will often pretend to be intersested when they are not.) If this child is not relishing adult conversation, and actulally avoids contact with you, I would seriously doubt that Asperger or ADHD is his issue.
Kids with Asperger would do well to have the skill to copy any child, they can't or they would also copy thier behavior-which they don't! They have a basic inablity to generalize to the degree it would take to copy your children's fashions (they don't realize that clothing has style, for the most part, and few even care if they are clean or fit well, as long as they "feel" OK.) Nor would an Aspie require toys your children had, unless the toys were of a very small and specific, often strange narrow scope. One of the halmarks of Asperger syndrom is a very narrow and obsessive interest, one that they cannot stray from and will go to great legnths to talk about and are nearly always incapable of playing with other items appropriately- unless your children only have trains, or TV guides, encyclopedias, dictionaries, earth moving equipment, clocks, bugs, animals, or pokemon toys- which are the kinds of things that hold Aspies focus to near exculsuvity!
They would take that toy and talk about it with you, not your children, because they cannot understand that you are not fair game for play nor that it seems inappropriate for them to bypass kids their own age to talk to the Mom or Dad...this would be the typical presentation for an Aspie. They would also know A LOT about many things, but not enough to know that you are trying to send them any clue that you have something else to do, it will be as if non verbal communication is not there at all, because no matter how many hints you drop by pointing at your watch, or yawning, or moving toward the door, they won't get it.
Just saying, your descriptions do not sound like asperger or ADHD to me, except that this child has some issues with behavior and some of the behaviors you describe could be the same kinds of things you see from an impusive, frustration intolerant child with either ADHD or Asperger, but the behavior on it's own is not a symptom. The reason that child has the behavior could be very, very different and there are only so many ways that behavior can be expressed, even when something is the result of a brain disorder.
M.