While the family is approaching the pacemaker inside the grandpa, Amy's hair stand on their ends due to the electrostatic charge around them. However, her parents' hair undergo no change during this time.
When the shrunk family is inside the grandpa, we see that they are sized almost comparative to the size of the RBCs (red blood cells), which is about 7 microns, while they were navigating inside his blood vessels.
However, earlier when they were encircling the words on the newspaper, we saw their size was almost comparative to the newspaper print, which is a few millimetres or about thousand times the size of the RBCs.