I am using tesla k20 with compute capability 35 on Linux with CUDA 5.With a simple child kernel call it gives a compile error : Unresolved extern function cudaLaunchDe
You must explicitly compile with relocatable device code enabled and link the device runtime library in order to use dynamic parallelism. So your compilation command must include --relocatable-device-code true and the linking command (which you haven't shown us) should include -lcudadevrt.
This procedure is described in detail in the "TOOLKIT SUPPORT FOR DYNAMIC PARALLELISM" section of the Dynamic Parallelism Programming Guide pdf, available here.