Select the model then...
In the animation menu set go to Skin=>Edit smooth =>Paint skin weights tool then click on the option box.
Under the influence tab, select the hip or leg (the joint closet to the moving leg).
Under paint weights select add and then hold down LMB and drag the brush over the vertex in the leg to attach that skin to the joint, that should fix the problem.
Then do the same to the face except select then neck or head joint to bind the skin to.
Thanks for wasting your time reading this line.