It depends on whether, under the circumstances, he was negligent, or unreasonably careless, in separating the children or restraining your daughter, or whether he acted reasonably--essentially used reasonable force--and the fact that your daughter was injured was an unfortunate accident, but not his fault.If he used reasonable force and acted reasonably under the circumstances, given what was happening, the age and size of the girls, etc. then neither he nor the school would be liable. However, if he acted unreasonably or used excessive fault, then both he and the school could be liable, such as for medical costs, lost wages if you have missed work caring for your daughter, potentially some amount for pain and suffering, etc. In this event, if neither he nor the school offers you compensation voluntarily, you could sue them for the money.