I aggree with Crayola Kiddies... The child will adjust with time.

I transitioned my last 12 month old (a year ago now) in a few hours at a time a few days at a time. It was a 2 - 3 week transitioning process. She cried all day every day. She would sit at the front door and cry. She's eat ok, but nap was a disaster! As soon as she started full time she eased right in and she's been amazing every since.

This round of newbies I have coming in in the fall (siblings of the older ones ) I'm trying to reduce the transition time as much as possible. Sometimes the parents insist, but I'd just prefer to go cold turkey.