Efficient way to get child entity/key given a parent entity

[Joydeep Sinha]

I wanted to ask if there is a direct and efficient way to get the child of a parent entity.

I am modelling a follower/ following relationship(like twitter). So I have a user model and a message model. I have a Follower and Following model which have a user model as a parent.

So whenever a user writes a message(or say tweet), all his followers should be able to get that. In this case I need to figure out who are the followers of the user(who sends a message).

Any help is greatly appreciated