As they created their interactive Mother's Day cards, you could see that they were really becoming fluent with new technologies. What do I mean by fluent? I mean that they were able to start expressing themselves and to start expressing their ideas. When you become fluent with language, it means you can write an entry in your journal or tell a joke to someone or write a letter to a friend. And it's similar with new technologies. By writing, be creating these interactive Mother's Day cards, these kids were showing that they were really fluent with new technologies. 3:44 Now maybe you won't be so surprised by this, because a lot of times people feel that young people today can do all sorts of things with technology. I mean, all of us have heard young people referred to as "digital natives." But actually I'm sort of skeptical about this term. I'm not so sure we should be thinking of young people as digital natives. When you really look at it, how is it that young people spend most of their time using new technologies? You often see them in situations like this, or like this, and there's no doubt that young people are very comfortable and familiar browsing and chatting and texting and gaming. But that doesn't really make you fluent.
Judging from the definition he provided (be able to start expressing themselves and to start expressing their ideas) "became fluent" actually means "стали самовыражаться" but it sounds so damn creepy in Russian so I'd also choose "на ты" just for the sake of literacy and smooth flow, sacrificing a part of the original meaning (the ability for self-expression) while retaining the rest of the meaning given by Efreytor_S.

Actually "на ты" = "know something perfectly" or "get the hang of", maybe.