You can hide or blur a section of the movie in Auto Movie Creator using the Picture in Picture Transition.

First, add your video to the storyboard, then add it again in the next frame. Drag the picture in the picture transition between them, then preview the transition and move the picture in picture box over the child's face.

You can now apply two effects to the smaller picture - pan and zoom and blur. For the pan and zoom, position the rectangle over the child's face, and check the box for 'make start and end positions the same'. Then, set the properties for the blur intensity you would like.

You can also substitute the pixelate effect instead of blur.