  Quantum critical systems with multiple dynamics possess not only one but
several time scales, tau_i ~ xi^(z_i), which diverge with the correlation
length xi. We investigate how scaling predictions are modified for the simplest
case of multiple dynamics characterized by two dynamical critical exponents,
z_> and z_<. We argue that one should distinguish the case of coupled and
decoupled multiple dynamic scaling depending on whether there exists a scaling
exponent which depends on both z_i or not. As an example, we study generalized
Phi^4-theories with multiple dynamics below their upper critical dimension,
d+z_<<4. We identify under which condition coupled scaling is generated. In
this case the interaction of quantum and classical fluctuations leads to an
emergent dynamical exponent, z_e=z_>/(nu (z_>-z_<)+1).
