My five-month-old boy is very talkative, but until recently all the noises have been vowel sounds -- coos, creaks, squeals, and squawks, but not a single plosive or stop.

But yesterday, on Father's Day no less, he looked at me and uttered "da!" followed by a lot of other noises. I tried to get him to say it again, but instead he regaled us with the first consonant he mastered, the old bilabial fricative. I'll try not to take that as personal commentary.