I'd go for the plasma.
Watching 3D repeatedly is actually bad for the eyes, especially for kids.
actually even for adults!
but still aim at 3D models - not because of 3D - but because they are the models with more features nowadays. Frankly, I just copied the suggestions from good evaluation sites
--- and more they told that these 3D things are just commercial hyping, features that hardly you will use in the long term. They just need to differentiate their products for now, and get more money from you - while you are salivating for 3D experience!
and they affirm what I wanted --- plasma is the best video display! LCD & LED can match plasma performance
but you will have to pay more than double
because LCD/LED needs more technologies inside to match the same performing cheap plasma!!!