I will not get sentimental, or so I keep telling myself. Well, maybe a little sentimental, but never maudlin at the approaching departure of my 17-year-old son for college in the fall. Fall? Did I say fall? No, he leaves in August — cruel calendar!

If I sometimes find myself leafing through photos of him at 2 and 5 and 11 — here nodding off in the stroller, there in his Harry Potter costume — and if there’s a smile at the memory of how enthralled the preschool David was with the Triassic, Cretaceous, Jurassic and its fearsome denizens, well, that’s the way of mothers. One video I happened to pick off the shelf featured an 8-year-old David narrating a tour of the backyard with, as he put it, grinning, “my dimwitted assistant, Ben.” That would be his little brother, who knew well how to give it back.