It's also worth pointing out that there are two kinds of belting recognised in the vocal anatomy world -
1) the strong, chestier mix that Mezzo is describing - it requires, as she pointed out, a very present tilt of the thyroid cartilage towards the cricoid - this lengthens and things the cords making higher notes easier to obtain with less pressure, then you place the resonance forward - principally in the mouth (although some people consider a nasal mix ok too - it depends on the music being sung) - which brings a really chesty sound to the overall product. The larynx here needs to be in a neutral position. This is very common in musical theatre styles and sounds great if done well.
2) The kind of belting I refer to 'safe yelling' - the larynx is placed in a very high position on purpose, then the false vocal chords are pulled back and phenomenal amounts of abdominal support are used (with a fair amount of back anchoring too) - this is effectively musical shouting. It sounds less harmonic-rich than number one, but i certainly louder and perhaps more appropriate when an actual yelled sound is required. Think Christina Aguilera.
Both kinds are perfectly safe if taught well and both have their place. Both are inappropriate for young voices, or even beginners, though - not so much for the thyroid tilt which is quite easy to teach, but essentially because if the support system isn't in place (particularly for number 2) the voice can be damaged through frequent mis-use of the techniques.
In Children, even if you do manage to teach the tilt (for number one) and the false chord deconstriction for number 2, so they end up doing it safely - the overall effect will be one of robbing the voice of richness and range over time.
It's not worth it on unmature voices or beginning singers. Icing the cake before it goes into the oven.
Allan
(Incidentally, I'm specialising in vocal anatomy for singing at the moment, so if you want any pictures etc to back this up and help you prepare for battle, please do PM me)