Many children have hemiplegia due to cerebral palsy, a stroke, or any other injury to the brain. Hemiplegia is when one side of the body has abnormal muscle tone and tightness due to a brain injury or stroke on the opposite side of the brain. In comparison, hemiparesis is when the person has muscle weakness and "floppy" tone (AKA flaccidity) due to the same reason. This means if the person has a stroke on the left side of the brain, then the right side of the body will be effected. The person loses not only muscle strength, mobility of the joints, and coordination but also sensation. When a person doesn't have full sensation in a limb, then they tend to not use it. For adults with this problem if they have normal cognitive skills, they can force themselves to use the arm and leg on the involved side of the body. Also, an older child might be able to do this. But for infants, toddlers, and young children this is not typically the case especially if they had the brain injury in utero and never had typical movement of the involved side of the body. Physical and occupational therapists have strategies they can teach the child and parent to aid in the child using the arm and leg, but sometimes this just doesn't work, because the child wants to use the other side because it is easier to use and it has full sensation.
Some children who have hemiplegia may benefit from constraint Induced Movement Therapy (CIMT) which is the technical word used for "forced use". The following link has links to various articles and research that has been conducted on the effectiveness of this approach with children.
Children's Hemiplegia and Stroke Association
I had a co-worker about 6 years ago who was conducting her thesis on CIMT. She set up a summer CIMT camp at the clinic we worked at in which several school-age children with hemiplegia participated. They had their non-involved arm casted so that they weren't tempted to use it. This "forced" them to use their involved arm which was hypothesized to build strength, coordination, and sensation. Certain criteria had to be met just to participate, because if the child had too much spasticity or other problems then CIMT wasn't going to be able to help. CIMT is not for children who can't use the arm at all (complete paralysis); there has to be at least some movement.
The end results of the project were good. Although every child made progress, I am not sure that any of them achieved completely "normal" use of the involved arm, but I do know they all continued to receive weekly OT and PT to build upon the progress that was made over the summer.
I have not ever used CIMT with the toddlers that I work with at early intervention (ECI), because I think they would just be frustrated and confused. Maybe a child in preschool or early elementary age would better understand the purpose of CIMT and not get so frustrated. However, I do "hold" the involved arm down for an activity as well as place toys to that side of them so they are more likely to use the involved hand instead of ignore it. Other techniques I use with young children with hemiplegia or hemiparesis include: NDT handling, bimanual activities, electrical stimulation, dynamic and static splinting/orthotics, kinesiotaping, adaptive equipment, infant massage, and sensory integration therapy. My favorite dynamic splint for infants is the Joe Cool (TM) splint, but they tend to not be as effective with the toddlers because they have figured out how to unstrap the velcro! The most important thing in helping infants and toddlers with hemiplegia/hemiparesis is teaching simple therapy techniques to the caregivers and parents because they are the ones who are primarily with the child all day long. For some of my kids who attend daycare in large classrooms and have parents who work long hours, the techniques asked of the caregiver might be simple such as making sure the child wears his hand splint during table-top and "centers" activities. I also suggest that at snack and lunch time that food and drinks be placed to the center and each side of the child to increase the chance that he may use his more involved hand; if the food and drinks are placed only on the non-involved side, then the child is not likely to use the hand that needs to get stronger. These are simple and do-able suggestions! If I give complicated strategies, the caregivers are not likely to have the time to perform them.