In Hansen & Reetz-Kurashige (1999), Hansen cites her own research on L2-Hindi and Urdu attrition in young children. As young pre-school children in India and Pakistan, the subjects of her study were often judged to be native speakers of Hindi or Urdu; their mother was far less proficient. On return visits to their home country, the United States, both children appeared to lose all their L2 while the mother noticed no decline in her own L2 abilities. Twenty years later, those same young children as adults "comprehend not a word from recordings of their own animated conversations in Hindi-Urdu; the mother still understands much of them" 

Yamamoto (2001) found a link between age and bilinguality. In fact, a number of factors are at play in bilingual families. In her study, bicultural families that maintained only one language, the minority language, in the household, were able to raise bilingual, bicultural children without fail. Families that adopted the one parent - one language policy were able to raise bilingual children at first but when the children joined the dominant language school system, there was a 50% chance that children would lose their minority language abilities. In families that had more than one child, the older child was most likely to retain two languages, if it was at all possible. Younger siblings in families with more than two other brothers and sisters had little chance of maintaining or ever becoming bilingual.

प्रतिगमन गृहीत-कल्पना The regression hypothesis (last thing learned, first thing lost)
प्रथम(पहिल्या) भाषेची झीज (FLA)
L2
L2 attrition