Saw daycare provider forcefully sit a child down?

I think you should bring it up with her supervisor. It seems as though she was being too aggressive, considering the child's age, but we don't know what happened. It may be that he was endangering himself or others in some way, such as climbing shelves repeatedly, throwing toys, or biting. If such behaviors are occurring frequently, maybe she was frustrated or having difficulty finding a way to stop the dangerous behavior. This is a high-stress field to work in and she may need some assistance finding ways to control dangerous behavior before a child hurts himself or another child or her. When you bring it up, try to show concern for her state of frustration and suggest that she may need some help. I know if I was maxed out on a child's behavior I would certainly appreciate some one intervening to provide some support. (Where I work, we work in teams for this very reason...if one of us becomes frustrated or unable to work with a certain child, the other steps in!)