Plz take him to a nearby pet hospital to get ultrasound or xray done, depending upon the location and size the further course of treatment shall be decided

Diarrhea or vomiting after the consumption of indigestible materials like plastic indicates it is causing GI tract issues as a GI foreign body. Your kitten needs further confirmation with X ray/ abdomen ultrasound. Once it is diagnosed based on the nature and location of the plastic materials, treatment options will be selected. Some cases it will come in motion, but in some cases, it may need surgery.