Buying a bottle for child is not a simple act. At shop there are a lot of theese items - made by many producers in many different colors and sizes. A bottles also differ from each other according to shape and using possibility.
You can buy normal bottles and match capacity with child's age. Why do we take too big botte when baby couldn't eat so much? Next case is colic possibility. When baby gulps air during wating colic can be out. That makes little emboli and could be troublesome. There are non-colic bottles - they are safe.
For older children we buy bigger bottles or water cans. Theese items are useful on walks.
Remember - You have to strerilize all bottles!