I know you asked for a sisters opinion, but I would like to think I have something to contribute to this question. I would trust your mother, unless you have been given reasons not to. I don't believe this incident to be such a reason. Accidents do happen! No matter how closely a child is being watched, they are still going to fall & bump his/her head. This will happen in even the most expensive & professionally run day care center. What you won't get at any day care center is someone who will love your child like their grandmother. It is a blessing to have one's parent be able to care for their child. My parents live 2 states away, and my in-laws live in another country. My wife and I would kill for one of our parents to be able to care for our daughter. We now pay $1000 a month (not including diapers & food) for day care. This is our 2nd biggest monthly expense (behind our rent), and it will double with our second child on the way. We would kill for an opportunity to have either mother here. I don't think you realize exactly how fortunate you are. In my opinion you should apologize to your mother, and hope she accepts.