The first day my oldest daughter went to preschool, aged three, her response once in the gate was' "Bye mum, you can go now." From that first day, until now, she has had no problem leaving the nest, as long as there are children & things to play with.
Our second child was a bit slower, but it took very little time for him to get excited about being at daycare one day a week. In fact, he was so excited that the lady running the daycare decided he was to excited to stay, "to active" were her actual words. So he was expelled from daycare at two. Although, he is now well settled in a preschool, and is looking forward to starting big school next year.
Our third child will not have anything to do with daycare, he's not quiet two yet. His response to a room full of toys and other children his age is to cry for mum & dad. Today, mum tried leaving his stroller at the centre for security, so he sat in it and cried for mum & dad. The lady running the daycare pushed him, in the stroller, close to some toys and books (at home he loves books and often just sits and reads one, well he's not really reading. The other thing he really loves are balls, he can already throw and kick well.). His response was to get out of the stroller, push it back to where mum had left it, get back in and cry for mum & dad. At this point mum got a phone call and our youngest son was soon home and happy, and reading books.