The "New Kid"

I will admit that when I went into school this morning, the last thing I expected was a new student. But in he came while I was preparing the classroom for the learning activities today. His mother accompanied him, informing me that her son had moved schools several times now, & that he was particularly sensitive. She also mentioned that he was going through "puberty." (I put that in quotation marks because I'm not exactly sure how a 10-year-old is already experiencing that, but I just let it go.)
When he went to another classroom this afternoon, based on his English language-speaking level, he ended up next-door to me. Apparently his phone rang during that class, & he walked out of the teacher's classroom to answer it. When she came over & vented to me about the situation, I found it strange that he had done so. When school was over, he had to walk by my classroom, so I stopped him & asked why he'd answered the phone in the middle of class. He responded that it had been his mother, so he answered it. While I did not want to really rebuke him when that was his response, I still gently reminded him that cellphones are not permitted during school hours & he would need to check it into the office tomorrow. (What I was really wondering is why that woman called him when she knew he was in class. But I'll save that conversation for a later date.)
One of my students is becoming increasingly more like a student I had last year, in the tantrum-throwing sense. She threw her book on the floor today during the whole class reading, & pulled her hood up over her head. When I went to talk to her, she burst into tears & refused to take her hood off, at which point I asked her to go sign her card for not following directions. That only infuriated her, to the point that I had to send her next-door to write a letter home minutes later; many of her classmates were distracted & unable to focus & do their work.
Then one kid slept through nearly every lesson this morning. I made everyone do jumping jacks & Yoga after recess though, & felt like that might cure him. Surely it did not. He put his head back down on his hands, at which point I got very frustrated with him & told him that he's surely going to fall asleep if he keeps putting his head down. I was trying to be careful in the way I spoke to him though, because he wrote some pretty suicidal lyrics on the back of his self-evaluation sheet last Friday & I'm worried about him. What can you do?
I honestly wonder what I need to do for some of these kids who are emotionally unstable; it concerns me for them as well as their classmates (because it requires my attention & effort every time something happens.)