Never. Nor should they be indoctrinated into any religion before the age of 10, as it has been proven that this damages their ability to differentiate reality from fiction, as well as their self-esteem.
Only in very rare cases where it could seriously effect the child's well being or mental/physical health, and even then steps should be taken to be as truthful as possible and to work towards being able to tell the truth, as even kids have a right to the truth
Children easily get the truth in the wrong throat E.g. If they ask why you (respect person) won't play with them If you say this game is to childish for you they will think they are wrong for liking it even if it fits their very state of development