As long as a child CAN drink from a cup...and is still allowed to practise with a cup...sippers are fine.
If a parent says that it's time to get rid of the sipper...you should follow their wishes. HOWEVER...those wishes are for the parents' home...and for the parents' supervision. If you are looking after children, and you have a few of them, there are practical reasons for you to use a sipper cup at YOUR home. You choose what is used in your home.
One way to get around that...move from sippers...and get "flip and sip" rubbermaid containers...They are technically straws!
HTH
Kat
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DenMother Kat...and nursing student!

Mr. E 9 yrs...Missy B is 7 3/4 yrs!... Sugar the Dog IS Four.