Thanks. I think I will call the therapist and see if I can get an appointment for him. His behaviour is so confusing, it's hard to sort out.
On the one hand, there may be some serious feelings happening - for example, he asked me what it would be like not to see. Not just closing your eyes but if you couldn't see at all (as if you were dead). We discussed a little bit and I asked him if he was just curious and he said no, and changed the subject. Also, he told us that another kid at school had said something similar (about hating her life and wanting to die). This seems to be on his mind.
On the other hand, he's figured out how to use this kind of talk to push our buttons. E.g. He was playing his video game. Time was up (pre-agreed) for that activity so I had him turn it off. He kind of smirked at me and said "I hate myself and I want to die". I asked him if he was just mad at me for making him stop playing and he said he didn't want to talk about it and changed the subject. He does similar things to DH.
But mostly he seems happy and normal - running around, playing with his toys, joking with us...