COME ON FOLKS, THINK! 
You are forgetting that there are a couple of tools of the film maker's trade at work here that weren't around long ago.
The first is that either they had the kids record some likely dialog for the future films NOW so they could dub it in and mask older voices or...more likely...
Digital manipulation to increase or reduce pitch SLIGHTLY, just enough to do a compromise age between where they were and where they will be.
I don't mean something fake and hokey. I mean something you can't tell from the real thing.
I have software that allows me to take a stereo recording of my voice and "darken" it or raise it somewhat without changing the length of the recording. In fact, using a pitch expander, I can do a pretty convincing twin sister for myself. The trick is not to overdo it.
Oh and it also helps to have VERY good microphones too. Not plugging a cheap dynamic mike into your sound blaster, but putting a couple of stereo electrets into a mixer, and doing LINE OUT to your sound card's LINE IN for true high fidelity. And one last word of advice....good mikes are like good cameras. Good mikes don't automatically make you David Rose any more than good cameras automatically make you Ansel Adams. There is a trick to setting up a good environment and capturing good sound. For one thing, don't think with all the reverb in the world and darkening pitch shifts you can be Aslan if you get close to the mikes and talk softly. Imitating talking loudly without really doing it records way differently. You come out wimpy sounding. You have to do what Aslan does...stand back and SAAAAYYY it, LOUUUDDDLY. The recording will have entirely different characteristics because you won't record the "close by" things you do with your voice that make it sound wimpy when amplified and reverbed.
John
You are forgetting that there are a couple of tools of the film maker's trade at work here that weren't around long ago.
The first is that either they had the kids record some likely dialog for the future films NOW so they could dub it in and mask older voices or...more likely...
Digital manipulation to increase or reduce pitch SLIGHTLY, just enough to do a compromise age between where they were and where they will be.
I don't mean something fake and hokey. I mean something you can't tell from the real thing.
I have software that allows me to take a stereo recording of my voice and "darken" it or raise it somewhat without changing the length of the recording. In fact, using a pitch expander, I can do a pretty convincing twin sister for myself. The trick is not to overdo it.
Oh and it also helps to have VERY good microphones too. Not plugging a cheap dynamic mike into your sound blaster, but putting a couple of stereo electrets into a mixer, and doing LINE OUT to your sound card's LINE IN for true high fidelity. And one last word of advice....good mikes are like good cameras. Good mikes don't automatically make you David Rose any more than good cameras automatically make you Ansel Adams. There is a trick to setting up a good environment and capturing good sound. For one thing, don't think with all the reverb in the world and darkening pitch shifts you can be Aslan if you get close to the mikes and talk softly. Imitating talking loudly without really doing it records way differently. You come out wimpy sounding. You have to do what Aslan does...stand back and SAAAAYYY it, LOUUUDDDLY. The recording will have entirely different characteristics because you won't record the "close by" things you do with your voice that make it sound wimpy when amplified and reverbed.
John
