On what the burden applied for children with rare diseases in Islam?

In Islam, children are considered sinless and under Allah’s mercy until they reach the age of puberty [1] ,[2] . However, some children suffer from painful and fatal diseases such as Tay-Sachs Disease , Canavan Disease , or Spinal Muscular Atrophy (Type 1) , and pass away without ever reaching the age of accountability. These conditions cause immense physical suffering, even though these children cannot be tested morally or spiritually, as they are sinless. The Quran states, “Allah does not burden a soul beyond its capacity” (Quran 2:286) . For the children described above, if this burden is not a test for them, **to which part of their existence does this burden apply**, given that their physical suffering clearly exceeds their capacity?