How to remove child nodes in firebase android?

If you are using DatabaseReference for firebase

DatabaseReference dbNode = FirebaseDatabase.getInstance().getReference().getRoot().child("Node");

Here Node represents the child which you wish to delete

dbNode.setValue(null);

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If you are using a dataSnapshot

i.e., while you are working on some data change events

dataSnapshot.getRef().setValue(null);

To remove data:

firebase.child(id).removeValue();

You might do well to have a look at the Firebase documentation for Android btw, which covers this and many more topics.