Hi, my son is currently using a rubber tipped sippy cup. It's similar material to a bottle nipple. It's designed for 12+ months so I'm assuming that it's not necessarily bad to still be using at 18 months but I'd like to move onto a straw cup. He enjoys straw cups and also uses this cool cup that teaches how to sip from a regular cup without spilling. No idea what it's called. However, I like him to get a certain amount of milk and he won't drink enough from the other cups. He will drink every last drop if he uses the rubbed tipped one. Is it okay to keep using the rubbed tipped sippy cups? Is it doing any harm? How do I transition to an alternative cup and get him to drink it all? He only likes to take tiny sips of water from the other cups. It would take him all day to drink 8 oz from the non-sippy cups. Again, hope I'm making sense

thanks.
Re: Sippy cups