That might be changing

Christina Ricci, Anna Paquin, Scarlett Johansson, Mila Kunis (by age), are bucking the trend and being successful as adults after being successful as children. It is too early to predict, but I think the current crop of Disney and Nick teens is too large for nothing to come out of it for the long term. The last generation (with the partial exception of Justin Timberlake) only lasted in music, but I think this generation will last in acting too. And of course, it's essentially granted that Dakota, Kristen, and at least Daniel and Emma from Harry Potter, have the all the good cards for lasting as much as they want.