To update you on a couple of loose threads:
She has not yet worn the underpants to day care. Several of you pointed out that the key thing will be the teachers' reaction, and I think that's right. And I know the teachers there will back up any girl's right to wear train undies, no special request required. She just hasn't chosen those on a day care day. Yet.
A head-in-the-sand approach is proving similarly effective with the baby squishing problem. I realized the other day (probably as a direct result of listing, in that post, all of the contortions that A and I have done in response to this behavior) that our response has been escalating as it's gone on, and that the goal of our response has been: Make it stop.
Not a bad goal, in theory, when the baby's rib cage is in constant danger of being crushed. But everything we've done with that end in mind has failed.
So now I'm looking at it this way: for whatever incomprehensible almost-three-year-old older-sister reason, Ingrid is sometimes just not able to control the impulse (desire?) to squeeze the bejeesus out of her baby sister. She is not going to stop it. She is not going to explain to us why she is doing it. So instead of getting our blood pressure all out of whack trying to get her to cut it out, we should be aiming to (1) make sure Ingrid knows it is not ok with us when she does it and (2) keep Iris safe.
So now Iris has a lot of play time in the crib, which she seems to love (she plays peekaboo with us through the bars and laughs her head off) and which keeps her away from the squish monster. When the two of them are close together and Ingrid begins to lose her gentleness, I say We don't do that, separate them, and ignore Ingrid in sort of a low-key way. No punishment, no long explanation, and no extra attention.
Is it working? I don't know. Iris is still alive, and I am less hoarse.