Thanks for writing to health care magic.
If your kid is having vomiting
and loose stool
please monitor him for signs of dehydration
1. Decreased skin turgor
2. Increasing thirst.
3. Sunken eyes.
6. Decreasing passage of urine.
Pain around the anal region could be because of a rash because of increased moisture there. Request you to just look at the perianal region.
Hope this helps.