IIRC (and heavily paraphrasing here as this isn’t my specialty to say the least) most languages end up having about the same information density because most humans process language at the same speed. Some languages are spoken faster, but have less density in information, where others are slower but have higher information density. In The end it evens out, more or less

From that, without looking at other facts, I’d guess that babies learn it pretty much at the same speed, no?