Just from my experience (at work) it was often boys that struggled to adjust rather than girls. Studies have shown that girls often cope better because they receive a bit of extra "nurturing" in their play with other girls... whereas the boys tend to compete more for the carer's attention. Not always the case... but generally speaking. I know that my DD coped with family day care very well at the age of 2.5yo whereas my sons would have really struggled.