Thank you for your query on Healthcare Magic.
Generalized swelling of the body with ascites, hypoalbuminemia
and decreased protein in serum with a normal blood pressure is suggestive of protein loss from the body whether in urine or from the gut.
Most probably your child is suffering from nephrotic syndrome
in which fluid retention with loss protein will be there in urine.
In addition to this he is having gastroenteritis
Nephrotic syndrome patients are more prone for dehydration
as they have low intravascular fluid volume to shift of fluid into third space.
Maintain his hydration by giving sips of low osmolarity ORS like Pedialyte to maintain hydration.
Monitor his urine output and daily weight.
Consult your Pediatrician
for the examination, assessment, investigations, and treatment for both conditions.
Hope I have answered your query.