This is the second batch. They are about 4 or 5 inches tall.
The first batch is (understandably) bigger, and I felt that they were ready for pinching-out. The books advise doing this when the plants have formed 3 to 4 pairs of leaves (which these have).
Now, not being an expert on such things, I have read-up about pinching-out. You do it in order to make the plants bushier, because when their main growing point is removed they put up sideshoots from lower down. Some plants do this naturally, like this one, which already has two stems:-
Others have to be persuaded. All you do is literally pinch-out the growing point with your finger and thumbnail. Pinch the main stem, not a leaf-stalk - like this:-
So there we are, let's see what they make of that...
By the way, I am quite relieved that my Sweet Peas survived the latest big storm last week. I had weighted-down their mini-greenhouse with copious quantities of bricks, but I was still worried. In the event, the greenhouse moved about a foot horizontally, but it didn't take off. Phew.