My 25 month old doesn't know how to suck from a straw either, mainly because he doesn't have the chance to try 😅
He doesn't drink anything that requires a straw, neither do we provide packet drinks/straw bottles etc so he didn't have the need to.
If your child needs to drink from a straw, he will learn how to eventually! We're transitioning from his milk/water bottle (with bottle teats) directly into open cups and bottles like what adults use so we have no actual plans in teaching him anytime soon - he can learn it when he needs to, but I don't see the need for a straw just yet :)
Anonymous