We study the decay of D0 and Ds+ mesons into five-body final states
including a KS0 and report the discovery of the decay mode Ds+→KS0KS0π+π+π−. The branching ratio for the new mode is
{Γ(Ds+→KS0K−π+π+)Γ(Ds+→KS0KS0π+π−π+)} = 0.102±0.029±0.029.
We also determine the branching ratio of {Γ(D0→KS0π+π−)Γ(D0→KS0π+π+π−π−)} =
0.095±0.005±0.007 as well as an upper limit for {Γ(D0→KS0π+π+π−π−)Γ(D0→KS0K−π+π+π−)}
< 0.054 (90% CL). An analysis of the resonant substructure for D0→KS0π+π+π−π− is also performed