I think babies should be put in contact with as much new languages as they can, basically through sounds and games, somehow preparing the brains for further language studies.
what about games? Babies need to play. And sounds? Just continuous sounds of other languages. No matter if they understand or not. At times, when I write, I like to have TV on. I watch a German channel which times to times have programs in French (arte.tv, an excellent channel). But I got aware that through that unconscious learning (my mind occupied by other things), German entered my mind as if changing tee-shirt and that now I can spot words in German. Babies are champions at learning-many-things-as-the-same-time. That's why listening many different languages when baby prepares their brain to easy learning. But maybe it's a bit too much to ask them to understand.
I think that babies can understand way more than adults give them credit for. Babies understand things well before they can speak.
When my daughter was a baby still in the crib, well under a year old, we went to grandma and grandpa's house. It may have been her first time there. We put her in the crib for the night, but she was very fussy. So I said, we'll be right next door, now go to sleep. That's all it took. She just wanted to understand where we were going to be, in this strange new environment. That explanation calmed her instantly.
I also remember her listening and understanding the weather report from the radio, when she was just learning to speak. Who knew she was even listening, let alone retaining what was being said?
So I'm pretty sure babies would benefit from hearing other languages spoken, from a very early age. The only problem I can see is that this listening may go to waste, if the exposure to these other languages ceases before a certain age. If the language exposure ends before, say, 6 or 7 years old (you can probably find better estimates from actual studies), it gets forgotten. Then you have to start from scratch.
But absolutely, if a language is learned at that sort of young age, the little person will learn to speak with no accent. The cadence and intonations will be just right. If instead you wait beyond 8-10 years old, then it's much harder to avoid speaking a foreign language with an accent. It takes special coaching, to lose an accent, when learning later in life.