How can it be small hand luggage if it already exceeds the fairly generous allowance KLM set?
If you are over the allowed size then they are within their rights to charge you and ask you to tag it for the hold.
>>we only have small cases by comparison to some<<
How do you figure that if again they are oversized? To be honest KLM are not that fussy but a lot depends on the gate agent especially on the return journey from Quito and how busy the flight is. Again you could be charged extra.
How much over the limit are you? For Equador you are allowed 2 checked bags each up to 23kg and 62"
By the way when posing these questions it is useful for you and us topost your destination eg B'ham to Quito. Saves people looking it up.