What would the starting food for a kid?
After the child's pediatrician OKAYS it, you can start on extremely runny Gerber baby rice cereal mixed with breast milk or formula- that's usually around the 4-5 month mark. My son's pediatrican said to go ahead with the cereal at 4 months because he was constantly hungry, lol. And then I introduced fruits/veggies at 5 months, again, after I checked with his pediatrician. All babies' requirements are different.
That depends on the age of the child...
If you literally mean 'start', then breast milk or formula is all a baby should have.