Normally the Key To The World will indicate ADULT or CHILD on it for both Park Admission and Dining on it. I have seen people with a child less than three attempt to use a KTTW for that child in the turnstile and it rejects as being a room key only with no Park Admission. Where the KTTW would normally show CHILD or ADULT now shows, for the under-three, INFANT. In the past an infant under three did not get a KTTW. I think Disney is starting to do this to confirm that the child is under three and entitled to free Park Entrance and free buffets, etc., and to indicate that if food is ordered for them at Table Service it is not part of DDP but has to be paid for. Note this last is my opinion only and is not official.