It is the duty of the father of the child to provide teachings of christ. Create a christian devotional atmosphere in the house. Give more importance to family prayers, rosaries, visiting shrines , charismatic retreat centers,etc. In fact it will attract this non catholic mother and her family to catholicism. He should view this as a golden opportunity to teach the teachings of christ to this non catholic family.
In my opinion marriage with non christian is not ideal. But what happened is happened. Look at the life of St Augustin . His father is a pagan and His mother is a christian. It is through the prayers and life of his mother St Monica that he became attracted to christianity.
If father of the this kid is not interested in providing him catholic faith, he will be responsible for the loss of the Soul of that Child before God.
We cannot blame the mother of that kid and her family, from their side they are teaching their kid what they believes. Also these pandits (brahmins ) are very deeply religious persons in india comparing to other castes in india.
Also we should notice that Sr Nirmala , the successor of mother theresa was a hindu brahmin and later attracted to roman catholicism because of the life of mother theresa.
I will give you one link. It is a website of a catholic charismatic lay men group providing life of jesus and new testament in the form of cartoons for kids.
You can down load the sample clips from this site or you can order DVD's from them. Really it will be a great help to teach that kid about life of Jesus.