My vet advises this treatment for kitten with poorly tums:-

Withold all food for 24 hours (difficult but necessary).
Make sure cooled boiled water (not straight from tap) always available.
Introduce cooked chicken cut into small pieces (no rice) and feed only this for couple of days.
Gradually introduce back to regular food by mixing chicken at 50/50 ratio over a couple of days.

This has worked for mine ....rice has always made their poos very runny and yellow so I would leave this out!

Hope your poor kitties are better soon