My eldest was 20 months when we sent him to his first playgroup in Singapore, which was 4 hours a day, five days a week. The nursery had a policy where the parents could only pick-up/drop-off - absolutely no hanging around! He bounded in happily the first two days, excited to play with new toys and new children. After that, he realized that we were missing until we came to pick him up, so there was a little fussing and anxiety expressed for another three days, but it took only a few minutes to allay. He's never had any problems since and look forward to school happily every day. I think it's tougher if the school doesn't have a consistent policy for all its students - allowing some parents to stay if they want. Can you imagine how confused the children must be? Even the children adjusting well must wonder why their parents didn't stay when other children's parents did. I would recommend finding a school with a consistent policy - either one that compels all the parents to stay for the same duration or one that prohibits them from staying at all.