I work in early years. Yes babies have a great understanding of body language and facial expression long before they can talk to communicate.

Young children are actually far more intelligent than most people give them credit for. Just because they can’t communicate it the same language as us yet doesn’t mean they don’t know what they’re doing.

If they didn’t understand body language, how would they bond with people? And people bond back with them? Not to be insulting, but it’s like with pets. We can build bonds with them because we learnt to understand each others body language even though we don’t speak the same language