No experience with IAD-IST but AFAIK you should have a state of the art 777.
With 24+ layover IST tour & hotel are complementary.Go to the hotel desk after immigration.You'll find further info in the '' complementary hotel for transit pax ''thread in this forum.
IST-ISB you'll get a 12 year old 738,no AVOD.Flight time about six hrs.
You'll have full meal services on both flights,Alc.and soft drinks are complementary.
As for ISB Airport you may need patience & a little recklessness.
TKs service is usually hit or miss.Never travelled with a child on this route but IST-ISB can become exhausting especially when Y ( quite often ) is packed.