you can count children this way.
databaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot snap: dataSnapshot.getChildren()) {
            Log.e(snap.getKey(),snap.getChildrenCount() + "");
        }
    }
    @Override
    public void onCancelled(DatabaseError databaseError) {
    }
});
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solved how can i get the count of key , value pair in firebase? [closed]