My (just turned) 1 year olds now prefer to drink out of straw cups. We've been buying the largest sized tommee tippee flip up straw cups but they don't hold enough liquid and I feel like I'm refilling them every 5 minutes! Does anyone know if there's any reason why I can't give them a different kind of straw cup, i.e. one for older toddlers, or older children? Do they have to be specifically for babies? Or can anyone recommend a larger straw cup that's age suitable?