thanks for query,
It seem that your son is having dysentery
,amoebic or bacillary type.
He requires anti amebic and antibiotic treatment like Ofloxacillin,metrogyl
Consult your doctor and get prescription.
Give him anti spasmodic like dicyclomine
Give him light diet,curd,rice,buttermilk and plenty of water.
Ok and bye.