this calibration problem occurs often with a damaged screen.
If one of your kids has ever had a DS you will note they are more susceptible to it (kids aren't as gentle with their toys).

I've not lost positioning on my screen, but i lack sensitivity.

Now, you could check theres nothing caught in the gutter (grit/protector etc) and if its still off by a large factor and not calibratable, then it sounds like a proper hardware problem.

I wonder if it would be possible to create a proper displacement map driver (pair of glasses) to rectify the problem for those out of warranty?