I would have to say that your son is already showing signs of not adjusting well. However, it usually takes up to three weeks for a child to adjust to their new situation. In this particular situation, I would not give it three weeks. I would have to agree with Heather on this one and pull him immediately.
I have been an inhome daycare provider for 2.5 years and I worked as a preschool teacher and director for six years. These things should not be happening to your son, especially in his first week!!!! I know that I loved and cared for EVERY child that was ever in my care, but that is not the case for all providers.
Last fall I went back to work for the first time in five years. I was a preschool director "in training." I saw and heard things that broke my heart. I lasted a little over a month and then called the state on them. The owner was great at putting on a her best fake smile and brushing things under the rug. I hardly think that smacking a child's mouth, calling the kids "losers," holding children's hands behind their backs to get them to go to sleep are things that should be swept under the rug. My daughter was attending there too and I have a full list of wrongdoings that they did to her, but I did not report those, as I wasn't sure if I was being too sensitive or not.
My point is, what kind of research have you done on this center? Did someone refer you to them? Ask the other parents how they feel about the center (without talking about your experiences). You, MUST, for the safety of your child, research, research, research until you're blue in the face. It is funny how so many people continue to go to centers that are mistreating their children and then they are furious when something bad happens like a baby with shaken baby syndrome or heaven forbid a death. This is not okay. You are the parent and your job is to protect your child. If you feel that he is being mistreated, then it is your right to pull him from the center immediately and move on.
I wish I could say that home daycares are a better solution, but they aren't. I would suggest finding a center that has video cameras to monitor your son in his daily activities. This will give you a better picture of how he is adjusting. Unfortunately, these too can give a parent a false sense of security, so please still do your research on the facility.
I will step off my soap box now, but please, if you feel your son is not adjusting, find another center. There are so many options available!