How old to appreciate IOA and Universal

[M]

We are planning a trip in Jan 2002 with kids 12/10/7 at that time. They are all extreeme rollercoaster lovers but two of them don't want anything to do with scary movies ie Jaws and Jurasic Park. Should we give up days from WDW for Universal and or IOA? How old do you have to be to enjoy these parks? Are there any heigth restrictions in these parks?

Thanks