The answer is that the children are touching and there is no gap between them to allow another child to jump the rope. This problem can be solved mathematically using the equations for a catenary cable however, in this case, only some simple logic is needed. If the rope is held at the top of the children’s head (120cm above the ground) and the bottom of the rope is only 20cm above the ground, then the rope is sagging 100cm. Since the rope is 200cm long, a sag of 100cm would mean that the two ends of the rope are touching and the rope is hanging vertically because a sag of 100cm is half of the ropes’ total length. Therefore, the span of the rope between the two children is 0.