In the last couple of weeks, my DS (5 years old, autism) has started hitting other children at nursery. Sometimes it's in response to them taking something from him or them having something he wants. Other times it seems completely unprovoked. Nursery have been quite understanding but took me aside on Friday to say that they'd started putting him into timeout when he did it, and that he'd had 3 of them on Friday. He's only there for 2 and a half hours! 
At home, we've had issues too. He has started a high pitched scream when he is told off for something, and he'll continue it for as long as possible to get a reaction (which we don't give). Eventually, (once I've got ringing in my ears) he'll calm down and ask for a cuddle or say he's sorry. We then have a very brief window to talk about it before his butterfly mind flutters onto something else and his attention is gone. He does hit DH and I, but only ever when he has done something wrong and we're telling him off. There are occasional scuffles with him and his sister (she's 3), but no worse than usual sibling stuff.
He has always been a very affectionate boy, and we've never had a 'hitting' phase before. If anything, we was too passive as a toddler and would let other children take things from him without ever putting up a fight.
Why would he be starting this now? Is he going through a phase that most children do, just that he's doing it later? Is it a normal thing for 5 year olds, but he's doing it to the extreme?
And what should we be doing? I am reading 'the explosive child', which makes a lot of sense but I'm not very far through yet and it seems quite a 'languagey' approach, which I'm not sure we'd be able to implement. Has anyone been through similar? Will it settle down?
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to anyone that has made it through my enormous post! 