I thought you might like to read Patrick Allen’s short article about the brain benefits of being multilingual. He’s responding to the video on this topic from the excellent TED-Ed video channel. You can watch the video here.
Personally, I have no doubt that being multilingual as an adult is beneficial in all sorts of ways. But I have my doubts about the merits of multilingualism among young children, below the age of 7 or so. What I mean is this: if young kids are in a multilingual situation this will do them no harm, but, other things being equal, I wouldn’t force kids to be multilingual at a very young age for no particular reason.
In fact, the most pressing need for kids to be multilingual is often quite intimate, as I have seen from my own experience. If kids cannot speak the language of their grandparents or cousins, they find it difficult to cultivate meaningful relationships with these relations. That can be a great pity!