Thanks for writing your query.
will decrease the vomiting
,but you should try to cure the underlying cause of vomiting.
After reading your post, it seems that he is having some infection in his gastro-intestinal tract, which is also causing loose motion
If the infection is cured by proper antibiotic or antiamoebic, its symptoms like loose motion and vomiting will also get cured.
I would suggest you that you should get his stool examination done to know the type of infective organism and start the medicines accordingly after getting him examined clinically by his Paediatrician.
I hope this is helpful to you.