Winston's essential thought crime is believing that rebellion against Big Brother is possible. It is tied in to his inability to totally believe all the things that he is "taught" about their society, some fleeting memories that he is unable to eradicate.
Another thought crime is believing that there is hope in the Proles, hope for a new social order. Although we know that this it total nonsense, thoughcrime is not based on reality, but on the inability or unwillingness to control thoughts that are contrary to orthodox belief.
The inability to see that 2 + 2 can equal anything the state wants it to equal isn't necessarily thought crime, but insisting that his perception of reality is real rather than the state's is a kind of thought crime.
These are all a lot more serious than what Paron's children turned him in for ... though crime can be very simple or very shallow, but it's all rooted in doubting or questioning the state's reality.
Although there is no thoughcrime in our world, I think there is a link in politically correct speech and some of the things that could be coming ... just an opinion.