Can't Always Get What You Want

Aaron has become quite willful of late.  When he wants something and you won't let him have it, he will throw himself an all-star tantrum. 

It could be something good - "I want my milk, and I'm furious I have to wait 45 seconds for it."  It could be something neutral - "That piece of paper my sister was holding, I just have to grab it."  Or it could be something bad - "I don't care that my dad keeps slapping my hand for trying to touch the latch that keeps the stroller from collapsing on it." 

No matter: the will is equally vehement, the fireworks spectacular. Frustratingly, a common action item for him in such cases is to hit his big sister with his hand or whatever is in his hand.

I know we have to hold our ground with him, because the more he learns that his tantrums help him get to what he wants, the more tantrums we'll have on our hands.  So we're trying to nip this one in the bud.