hmm, the teat size seems to be right. Maybe try another brand. We tried different brands for my baby, and ended up he likes Dr. Brown teats, and would not drink from Avent teats.
last time i told u my baby also use 'NEW' NUK yellow 闊身樽奶咀!
she also take a long long time to finish milk ! becoz the air system si very very poor!
NUK