But if there is any object which will serve as a mark in sight, it seems to have the effect of drawing his aim towards it.

He shoots at the vane on the barn, at an apple on a tree, a knot in a fence--any thing which will serve the purpose of a mark.

This is not because he has any end to accomplish in hitting the vane, the apple, or the knot, but only because there is an impulse within him leading him to shoot, and if there happens to be any thing to shoot at, it gives that impulse a direction.
It is precisely the same with the incessant muscular activity of a child.
He comes into a room and sits down in the first seat that he sees.

Then he jumps up and runs to another, then to another, until he has tried all the seats in the room.

This is not because he particularly wishes to try the seats.