Thanks for writing your query.
Excess loss of fluid during diarrhoea
and excess urination can result in dehydration
and can be harmful.
Even if the diarrhoea has slowed down, you should treat the cause of infection.
Also maintain the hydration of the child by giving liquid rich in electrlytes.
Give him light diet for eating.
Also get him examined by a medical professional for dehydration and start medicines under medical supervision.
I hope this is useful to you.