Sippy cups keep the
cheeks & tongue in a primitive suckling position.
Muscles used to drink are also used to talk. Speech/Language Therapists say not to use them for preemies & babies with pre-language delay. If you hold a double-handled open-mouth cup for him at 10 mos., he'll hold it & drink it all while seated when weaned at 12 mos., when maximum recommended intake of milk & milk products is 16-21 oz./day