We review here recent numerical results concerning the acceleration and collimation of relativistic outflows from neutron stars, and we discuss their implications for models of magnetars in their hypothesized initial high rotation states. New results with different injection conditions and extending to much larger distance from the central star are also presented and discussed, showing that, only in the case of weakly magnetized winds, collimated outflows are indeed possible. We finally comment on the possibility that newly born magnetars might trigger GRBs, and we show that numerical results do not support such hypothesis.