A solution of the transport equation for cosmic rays in turbulent magnetic fields in a spherically symmetric geometry is presented. The results are applied to particle propagation in superbubbles. In the fully analytical calculation, various energy-loss processes are considered. From the distribution function of the cosmic-ray particles, the distribution for pions from continuous losses is computed. Folding with the appropriate cross section yields the gamma-ray distribution. It is shown that in the case of efficient acceleration the volume-integrated π0-decay gamma-ray emission from the superbubble exhibits the characteristic hard differential number density spectrum at large gamma-ray energies, Eγ > 70 MeV. This prediction is useful for identifying efficient superbubble cosmic-ray accelerators from gamma-ray observations.