Those children are as good as orphans already. People that age will not be able to cope with two small childrena nd it will undermine their health and bring them to an 'early' death.
As the parents have no other children, who will take care of the children when they die? Indian families are usually built around descending generations, not parallel generations, so collateral family will be less willing to take them in when their parents die, unless they can be made use of.
An utterly selfish act all about the parents and without regard for the welfare of the children.