Danger Mouse said:
I would take into consideration that your daughter is at the age where she'll be going to school most of the day as well, and that as she grows older, if she's like most girls, she'll have less time to spend with you (all that talking on the phone to girlfriends and
boyfriends 
... don't worry that's still a few years off

). Your schedules may coincide more and more. And there's nothing that says that the overwhelming majority of the time you can't spend a little while at home with her in the evenings and then do more work once she's in bed. As you say, you will still be able for the most part to set your own hours.
Truthfully, I have little doubt that you will do well by her no matter which way you choose.
To me, it would seem the bigger question is one you need to ask of yourself...would be okay being beholden to others in your work? While they are not your bosses, you do have responsibility to your partners, something you don't have now. You are only responsible to you and your clients.
As for your current clients and the panels your currently sitting on... is there no way to take them with you? Why must you give them up if you join the firm? It would be win-win for both the corporations and the partnership if you remained on the panels, wouldn't it? The corporations wouldn't have to find a replacement for you and you would be brining new business/connections to the law firm. Perhaps there is something I'm not understanding about it though that would preclude you from doing so.
Provided you are okay with being responsible to others to a greater degree than you are currently, I think the partnership sounds like a great opportunity.