Ooo, good suggestions! :-)
She told a story about Jonathan yesterday which was somewhat garbled, but the import seemed to be that a) he told her not to sit next to him, and b) he wasn't bothering her any more because she wasn't playing with him. She didn't sound dejected, though -- more intrigued, and perhaps a bit smug.
So I'm wondering, knowing my daughter, if she found some subtle way of retaliating by pestering him, and he's now fleeing her.
There are two Sydneys in playgroup, too. The one who is Aviva's friend, and the one who Isn't. The friendly Sydney said Aviva could sit next to *her*.