Hi Tamirra, my daughter was the complete opposite, but even thats not nice as I started to wonder if she preferred being at nursery to being with me - lol! Lots of my friends have had this problem with their kids and they were all told, by the staff at the various nurseries, that the child settled a couple of minutes after the parents had left, they have all settled now and go in without making a fuss (but for some it took months).
What do the staff say? Is there anywhere you could go and watch without being seen? The nursery my daughter goes to has CCTV that the parents can sit and watch for a few minutes if they're worried.
I don't think you're bing cruel, kids need to learn that they can't be with mummy all the time, nursery also helps them to develop social skils, and lets them try things that they may not do at home.
I think it's better that they get used to this before they start compulsory education - my nephew never really went anywhere without his mum, until he started school a few months ago, I don't think he's done a full day yet because he works himself up into such a state about it, that he is upseting the class and has to be sent home! His mother wishes she'd sent him to nursery, but she couldn't stand to see him upset when she left so she stopped him from going.
Good luck, things will get better!