My daughter is almost 8 and has cerebral palsy, dysautonomia, and autoimmune disease. Her dysautonomia causes her to be unable to regulate her temperature. In addition, it causes her eyes to be chronically dilated and her skin to respond in unusual ways to sunlight. Being in the sun for just five minutes will cause her skin to become very red, will increase her heart rate and blood pressure to dangerous levels, and will cause her oxygen levels to drop. If she remains in the sun any longer, her body temperature will begin to rise. She has to wear sunglasses outside at all times. She will get burned by the sun in only a few minutes of exposure.
We have experimented with commercial stroller parasols, and while these help somewhat, they are not particularly useful. Because of a lack of a sunshade, my daughter must stay inside on hot and sunny days. While her condition is definitely more severe than most, many children struggle with the same general problems.