How reliable is the testimony of a child witness?

X is alcholohic and sometimes beats up his wife Y This makes the wife lock the husband in a room in their house often and one night X is locked inside his room while Y was in another room of the house with both of their children suddenly, Y smells smoke and realizes there is fire in the room in which the X is while the door being padlocked, X succumbs to his injuries, and dies Can the children testimony after a decade viable enough to convict Y of her crimes? Children can attest to Y padlocking X very often.