Have you tried encouraging them to sit on the toilet longer to make sure it's all out?

Also Does the poo look normal and well formed without being to pebbly or soft? If its not formed properly, it could indicate a food intolerance or maybe not enough or too much of a particular food.

I think 5 poos is excessive. Maybe keep a food and poo diary for a week for each child as well just to see if there are any patterns. Then you could always take that to a doctor if you are concerned.