Mirror therapy, which provides the visual illusion of a functional paretic limb by using the mirror reflection of the non-paretic arm, is used in the rehabilitation of hemiparesis after stroke in adults. We tested the effectiveness and feasibility of mirror therapy in children with hemiplegia by performing a pilot crossover study in ten participants (aged 6-14 y; five males, five females; Manual Ability Classification System levels: one at level I, two at level II, four at level III, three at level IV) randomly assigned to 15 minutes of daily bimanual training with and without a mirror for 3 weeks. Assessments of maximal grasp and pinch strengths, and upper limb function measured by the Shriner's Hospital Upper Extremity Evaluation were performed at weeks 0 (baseline), 3, 6 (intervention), and 9 (wash-out). Testing of grasp strength behind the mirror improved performance by 15% (p=0.004). Training with the mirror significantly improved grasp strength (with mirror +20.4%, p=0.033; without +5.9%, p>0.1) and upper limb dynamic position (with mirror +4.6%, p=0.044; without +1.2%, p>0.1), while training without a mirror significantly improved pinch strength (with mirror +6.9%, p>0.1; without +21.9%, p=0.026). This preliminary study demonstrates the feasibility of mirror therapy in children with hemiplegia and that it may improve strength and dynamic function of the paretic arm.