I need your ladies advice!

I have a brother/sister pair in my care. They started a couple of months back. Both are part time. DCG is 18 months and here 4 days one week, then 2 days the next. DCB is here after school on alternate days.

Anyhow, starting this week, the DCG is hitting everyone. She will literally just walk up to someone an hit them in the head. If they react, she does it more. I think that she is doing it to just get the attention, but the kids are starting to get annoyed, understandably. The thing is, if I tell her no, (in ANY situation) she smirks, stops and no later then 1 minute later, does it again while looking at me. Again, I think that it may be an attention thing. So yesterday at pick-up, she started hitting a dcb (5 years) over the head while he was putting his shoes on. Her mom told her to stop and instead of stopping (like she does with me) she actually does her smirk and hits harder. Her mother thinks that she is picking it up from her brother.

Let me give you a bit of background of her brother. Apparently, the second day of school (JK), the mother got a phone call stating that she needs to get hi tested for autism. She was not happy that the school made that decision on 2 days of care but started to bring him to a psychologist. The doctor moved and she basically decided to leave everything the way it was, not getting him assessed. Of the very short time that I have had him, here are some of the behaviors that I have seen:

-he repeats the same question over and over "Where is mommy?" Apparently, he even does this at home while talking to his mom.
-he answers his own questions
-he asks 'why?' to everything
-he takes peoples food from their plates while they are eating
-he comes in from school, SCREAMING for mommy
-he will imagine that mommy is there at the door and tell me that she is
-he takes things from kids and when I tell him to give it back, he smirks (the same smirk as his sister)
-he will walk back and forth to my front door and couch, asking the same questions
-he will be screaming and a plane will fly by, he will stop, look at it talk about it like nothing happened and then start screaming again

He will do all of these thing for the full hour to hour an a half that he is here. The only time that he stops screaming and asking questions is when it is snack time, but lets face it, I am not going to feed him for hours!

There is more, but it is Friday and I dont feel like typing them out..lol

I have tried a number of approaches. Answering his question. Ignoring his questions. Directing the questions back to him. Diverting his attention. Nothing. Nada.

ANYHOW, back to the main point. The mom is very concerned that the daughter is showing a lot of similar traits as her brother. And the hitting is becoming a problem. What do I do? About the hitting? About the DCB? About mom? She is having a REALLY hard time with everything....