I used 1 until baby was 1. I would say stick to 1 and change to 2 if you want as flow is quicker
I changed my LO to teat 2 a few weeks ago he's only 9 weeks old.. he was falling asleep during his bottle and wakening up half an hour or an hour later screaming as if he was hungry still, he was sooking so quickly and I felt he was only taking an Oz when I looked at the bottle but you'd think he had took more going by his sooking my health visitor told me to try teat 2 ( give baby time to get used to it) will slever alot and look like they are getting too much too quick but they will get used to it just make sure babies sat upright and burp more often my LO is now used to the teat and finishes his bottles 🥰 it's worth a try won't do any harm xx
I used 0, few weeks later I went to 1. Now he's using teat size 2 but he's also using anti reflux formula which is thicker.