Thank you for your query.
This is not a specific side effect of Zentel.
I think you child is having an attack of gastroenteritis
Give him Ondem syrup for vomiting
syrup for his loose motion
.Add yogurt to his diet.
Avoid fruits,milk and wheat products.
Consult your doctor if the problem persists.
If you have any further queries you are free to consult me.
Hope this answers your query.
Wishing a speedy recovery.
Have a nice day.