C.,
he's too young for discipline.
see my other replies to posts on this - unfortunately, I'm busy practicing what I was talking about - simply repeating over and over what I WANT him to do, not what I don't want him to do..
the long and short of it is: YOU know what the word 'don't' means. He can't process 'don't' in a sentence and make it function as a negative equating to 'don't do this or you're going to get a really negative consequence.
You can see it because you've repeated yourself umpteen times.
he can't see it because a) he lives in the moment. B) he has very little memory for new things that are intangible. because it isn't something he can 'touch' with his hands, he really is at a loss for how to process it 'correctly'
but each and every time you say 'don't dump water on your brother's head' all he hears is the 'dump water on your brother's head'. So really, you can't blame the little guy for just following instructions...
and as far as consequences, you're taking away ONE toy. out of HOW MANY? Ummm.....
...and then the come back? It's just a complicated game of attention....seeking...mastering....question is... who is winning?
go back to the 1 year old idea (and I still do this for my 4.25 year old!) of repeating what you want, gently leading him away from dangerous situations, intervening between siblings by using your body not your words.
good luck, read up, and get on track with the little guy!
M.
PS: and my little guy just discovered that he knows how to break into child-proof bottles just like his older brother. SMILES!