Are CSPRNGs quantum-resistant?
The best generic attack against a PRG (i.e. an attack that does not use any internal structure of a construction and hence works for any PRG) is exhaustive search for a seed. I think this was not done yet but it is very likely that the optimality of Grover's algorithm carries over to this setting. This would mean that for $n$ bit seeds, the best attack requires $O(2^{n/2})$ evaluations of the PRG. 

For PRGs build from hash functions and block ciphers this should be the case also for specific, non-generic attacks (assuming the used hash / BC is post-quantum). Of course, if you use a number theory based PRG like Blum-Blum-Shub Shor's algorithm kicks in.