I think it's quite common. It's a phase both parents and kids have to go through.
I sent my son to CC when he was 18mths. He was ok for 1st 2 weeks and after that started to cry when he saw us leave. It took him slightly less than 1 month to understand that he has to go CC.
Now, after 8mths, sometimes he refused to go home !! At times when he has foul mood, he will still cry when he sees us leave.
I dont't have any remedy as usually when he cries, I leave him with the teacher to pacify