Card has stated that "children are a perpetual, self-renewing underclass, helpless to escape from the decisions of adults until they become adults themselves." Does Ender's Game prove or disprove this opinion?

Ender's case certainly proves this. Despite Ender's obvious maturity and intelligence, he is manipulated to doing the bidding of the military. Children are pretty helpless when it comes to deciphering complex manipulations by adults, especially when they have never seen or experienced anything different.