Questions

Our Solution:

They both lied.
The child with the black hair is the girl, and the child with the white hair is the boy.
(If only one lied they would both be boys or both be girls)

We know that 1 yard = 3 feet. 

A yardstick which is used for measurement has 3 feet long but it cannot walk.

The Chipko movement or Chipko Andolan refers to a forest conservation movement or deforestation. In modern india, it began in 1973 in the state of Uttar Pradesh (now Uttarakhand). Sunderlal Bahuguna and 84 villagers risked their lives to protect the forest trees from being felled on the order of the maharaja (king) and went on to become a rallying point for many future environmental movements all over the world it created a precedent for starting of nonviolent protest in India, and its success meant that the world immediately took notice of this non violent movement, which was to inspire in time many such eco-groups by helping to slow down the rapid deforestation, expose vested interests, increase ecological awareness, and demonstrate the viability of people power. Above all, it stirred up the existing civil society in India, which began to address the issues of tribal and marginalized people.

Chipko type movement dates back to 1730 AD when in a khejarli village of Rajasthan, 363 people sacrificed their lives to save khejari trees.