## Results
### Robotic Devices  
The literature search allowed us to identify a moderate number of robots (14) that were developed beyond the proof-of-concept stage and were actually used for upper limb rehabilitation of children with neurological disorders. In the next paragraphs, the robots are classified following the chronological order of design and briefly described according to some of their relevant features (namely, the type of device, the number of degrees of freedom (DoF) and the affected human joints). Figure 2 shows a graphic map indicating where the 14 selected robots have been developed and actually used. It indicates that, in most of the cases, clinical studies using the robotic devices for pediatric population were performed where the device was designed, with a few notable exceptions. For example _Armeo Spring_[44], designed in Volketswil (Switzerland) has been primarily used in clinical studies located in Italy; _InMotion2_[45], designed at MIT (Boston), has been used also in New York (USA) and Rome (Italy). Figure 1: The flow diagram of the number of studies included. The 14 selected devices differ in terms of type (exoskeleton or end-effector) and the sets of targeted joints (shoulder and elbow in most cases, wrist or hand in fewer cases). As regards the mechanical structure, the selected robots have a different number of degrees of freedom. As regard the control scheme, two schemes are used (impedance control [15; 45; 51; 52; 53; 54] or admittance control [47; 48; 49]) that are characterized by specific functional features: robots based on an impedance control scheme are highly backdrivable, thus allowing the users to move actively without being affected by friction and inertia of the device, and operate by measuring accurately the actual position and generating the appropriate force/torque output; in contrast, robots based on the admittance control are generally non-backdrivable, require force/torque sensing and inertia estimation, and operate by sensing the actual interaction force and providing the appropriate position reference as output. Table 1 stores a systematic presentation of the characteristic features of each selected robotic device. Let us list, here, a brief overview:  
1. _KINARM_[46] is a bimanual robot, which allows movements in the horizontal plane (2 D) targeting the human shoulder and/or elbow joints; it can be used in an exoskeleton or end-effector configuration;
2. _InMotion2_[45] is an end-effector robot for shoulder and elbow with 2 DoFs; it is a commercial version of MIT-Manus [57] and its configuration allows low impedance on the horizontal plane and almost infinite impedance on the vertical one;
3. _Armeo Spring_[44] is an exoskeleton with 5 DoFs with a rehabilitation target of the entire human arm; it is actuated by passive springs with the role of supporting the weight of the arm, allowing natural movements in the 3D space with a wide range of motion;
4. _ACT3D_[47] is an end-effector robot that allows movements in 3D space properly designed to treat shoulder and elbow; it consists of a modified 3D HapticMaster (admittance controlled robot for shoulder and elbow) [58] with an instrumented end-effector and the patient's arm is connected to the robot through a lightweight forearm-hand orthosis;
5. _NJIT-RAVR_[48] is a 6 DoFs end-effector device; it consists of a 3D HapticMaster [58] combined with a ring gimbal that permits 3 additional DoFs (orientation: yam, pitch and rotation: pronation/supination) of the forearm;  
Figure 2: A world map identifying where robots for upper limb rehabilitation have been developed (red arrows) and where they have been used for children with neurological disorders (black dotted arrows). The color filling the circular areas indicates the number of clinical studies performed in the specific locations. The robot selected are:_KINARM_[46]; _ACT3D_[47]; _NJIT-RAVR_[48]; _reHaptic Handle_[49]; _MyPam_[50]; _REAPlan_[15]; _ChARMin_[51]; _Arneo Spring_[44]; _PASCAL_[52]; _AMADO_[53]; _WristBot_[54]; _InMotion2_[45]; _IOTA_[55]; _Noviint Falcon_[56].