We used the smaller ones and kept refilling throughout the day, like Carolyn said. They were easier for Tyler to handle at first, and once he got a little older, we switched to bigger ones. I wasn't a big fan of the straw ones when Tyler was that age. He didn't learn how to set his cup down right side up when he was done instead of tossing it aside for a few months, and the straw cups spilled more than regular sippys when laying down or flying through the air. HTH!