You might want to recommend to your sister that she at least follow up with her child's pediatrician
to make sure that there is nothing serious going on.
is children is fairly uncommon, it can occur. For example, there are autoimmune conditions, such as juvenile rheumatoid arthritis, that can occur in children. Symptoms might include red or swollen joints, fevers, and rashes. It is also possible to get arthritis in children after a common infection, such as strep throat infection or a viral infection.
Your nephew's pediatrician will be able to perform a complete examination, looking for evidence of any joint inflammation or other concerning signs. Based on what is found, they may decide that nothing further needs to be done, or they may recommend some workup, which will likely include some basic blood tests.
If a workup is recommended, and the blood tests are positive for any evidence of inflammation, then the pediatrician may involve a specialist, such as a pediatric rheumatologist
, who is skilled in the diagnosis and management of joint conditions in children.
Start by encouraging your sister to take your nephew to see their pediatrician for a general checkup. Good luck!