AITAH?

Favoritism amongst children is disgusting and I personally think you have a reason to be upset at that But if you already knew that he favored your guys's oldest compared to the other two children then I don't know how you wouldn't have seen that being an answer eventually. However he may have listed her first as he stated because she is the first born and then maybe tomorrow he'll say the second but how you explained it, it doesn't seem like that's going to be the case so I would definitely feel some type of way regarding that.

I think the issue is more profound and should be addressed to him. It's not ok to show favoritism this way with siblings. I would expect maybe him telling about her today and about other kids other days as part of the exercise. I don't think it's bad. But if you see that in general he clearly shows favorite then he should improve and do better for the family

Was it his first time doing this exercise? With exercises like this, depth of reflection usually develops over time. Be patient.

I can't comment on the favouritism issue.

To try to see it from the other side, he's on day one of a therapy exercise and the first thing that's happened is you getting annoyed/upset with him which probably hasn't helped his confidence with it. Favouritism is a big problem if that's what's happening so I totally get it but I have to assume he's in therapy to improve himself so hopefully that will also be addressed. For me it makes perfect sense to say the firstborn first, but I'd definitely be hoping the second born to be second. Maybe discuss with him what your role is supposed to be with this exercise - is it better that you listen and then revisit later on if you have something to say about it, once you've both had a bit of time to think/be able to approach it calmly?

Maybe he wanted to name each child on their own separate day?

So it’s your husband’s therapist, not a couples therapist you both see, right? lol idk if I was your husband I might start just journaling my answers instead of saying them out loud.