Tata means bye in Urdu as well as several others languages, and bata is probably pronounced 'beyta' (pronounced like the Greek letter), which is an affectionate term used from an older person to a younger person.
July 5, 2015
TATA is same as you described but BATA is not. BATA is with no meaning. these words are used with no meaning purely to made a soft and playful sound of the previous word and they are made on the same pattern of the first word like Chaye-Waye, Biscuit-Wiscuit etc
I heard someone saying her child " tata bata" it is said to children to motivate them to say tata to others
I am not sure though.