Petitioner satisfied its burden of making an initial prima facie showing of abuse by introducing medical testimony establishing that the child had sustained a fractured left femur that was "of such a nature as would ordinarily not be sustained or exist except by reason of the acts or omissions of the parent or other person responsible for the care of such child" (Family Ct Act § 1046 [a] [ii]), and that the mother's explanations for this injury were implausible or otherwise unreasonable. Indeed, the mother failed to rebut the presumption of culpability with a credible and reasonable explanation of how the boy had suffered a broken leg ( see Matter of Benjamin L., 9 AD3d 153, 155), or otherwise to demonstrate why she was not guilty of abuse. Moreover, it is well settled that credibility determinations by the Family Court must be accorded due deference since it is in the best position to assess the witnesses ( see Matter of Irene O., 38 NY2d 776, 777). Inasmuch as the record contains ample evidence to justify the fact-finding of abuse, there is no basis for disturbing its order of disposition.