If you're referring to 'burn in' problems, as long as the TV isn't being used for extremely long sessions it'll be ok. I guess your son doesn't/ won't play for more than 1-3 hours at a stretch? Even if he were to go on for 5-6 hours (though I have doubts!), it won't be an issue.
Burn in won't be an issue unless you're leaving a static image there for well over a day straight, so to say. Even then, most of them are pretty good with that kind of thing these days. Burn in won't be a problem as it does take a while for the images to actually burn in and the screen has to be left on the same thing.
Purely from a gaming perspective, keep in mind that a plasma will cause alot of glare if there is alot of light in your room.
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I play on my 50" Panasonic Plasma, and to be honest, I take a break every 30 minutes or so to prevent this from happening,most games do not have a static image, but some do like health displays and huds, but then most sky channels have annoying channel icons showing permanently, and we have press the red button logo burnt in on our 4 yr old 42" plasma! so what the hell, go for it!