My son is two and half years old, I have a bite mark on my right arm to prove it, yesterday he cried for 30 minutes because he wanted something to be somewhere (I don't recall what it was...), and my wife gets really desperate when he repeats the word "mom" 10.000 times in two minutes
The terrible two are what they are
... though times for any parent.
I find that he gets very frustrated when he doesn't get our attention, and becomes violent, throwing things around, kicking the dogs, biting us, etc. The only thing that calms him down his getting our attention. So simple to solve, so many worldly obstacles on the way... Like cooking dinner or changing his dippers . At these ages there is no communication with the little ones, if I tell my son that I am very sleepy and I need to rest he replies "Play!! Cars!! Now!!" while jumping around, If I tell him not to play with the knifes, he starts running, holding the knifes, and challenging me to catch him.
When anger arises in my mind I yell at him, when he insists on putting a fork on the electrical plug I slap his hands. But when he gets very frustrated and starts crying and hitting things, humour is my best friend. When he cries I cry, when he lays on the floor kicking the air, I do the same and ask him if I am doing it right, or I aks him if he is done with it. He usually starts laughing and stops the wild behaviour.
Some diseases make the parental task even more difficult, in those cases I believe Bhikkhu Pesala's advice is extremely important. Don't try to carry too much weight on your shoulders. A close friend of mine has a child with Angelman syndrome, and support to the parent his needed very often.