The easiest way to learn a second or third language, would be in school. Many Indian schools are English medium, but kids learn at least one more language, as their 'second' language. Sometimes Hindi, sometimes Sanskrit or even a foreign language like French. In addition to it, we learn our mother tongue (assuming Hindi is not the mother tongue), so its easy to be trilingual.

There is one disadvantage though. Kids don't get to choose the language, its pretty much decided for them by their parents. When we learn as adults, we can pick and choose - depending on our goals.