Nowadays, after Yishion grown up and can speak quite well, he do not like to greet strangers.
He will call and greet to those like grandfather and mother, nearest aunties (mother and father side) and some mummy and daddy friends only.
But most of the time, mummy will force him at least to say Goodbye when going back. So he will....
I think that, if I do not teach him from now, next time he will not say Goodbye to all people include me as also..