what do you mean by changing the bottles? My boy is almost 6 months. We have changed the teats from slow to medium flow when he's 3 months and planning to change to quicker flow soon. But that's all, never intended to change the bottle itself.
We did use the smaller bottles when baby was young now that he drinks more milk we have changed to the larger bottles. It does depend on his appetite. I guess if you have used large bottles all along then there is no need to change.
our babies bottles?