Multiple fragmentation of small Na-n(+) clusters (n=3-5) induced by collision with He atoms is investigated in the 200 eV collision energy range. The Na-n(+)-->Na-n-2(+)+Na+Na channels are studied using a multicoincidence technique allowing for the determination of the velocity vectors of the three fragments. The relative contributions of the two basic mechanisms, namely the electronic excitation and the momentum transfer in elastic binary collisions between the He atom and a Na core are estimated. For Na-4(+) and Na-5(+) clusters the momentum transfer mechanism appears as a two-step process: The ejection of a fast Na atom in a binary Na-He collision followed by the evaporation of an additional slow Na atom. However the angular distribution of the slow Na atom is not isotropic showing that a partial memory of the initial binary collision appears in the evaporation process.