Yes, this is an unusual area for a child of 3 years to suddenly develop a rash. One of the worrying possibilities is an illness called 'Henoch Schonlein Purpura'. This illness may follow a recent infection but often the cause is unknown.Please take your son to an after-hours paediatric clinic to be seen.Please mention this possible diagnosis as it is often missed.
The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal
advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.