Answer: Unfortunately, it is not realistic for you to expect to work "banker's hours" while striving for partnership (or simply striving to stay employed) at a "biglaw" firm.
After you became a parent you may have been surprised at the lack of sympathy and understanding you received from your firm. Especially since many firms tell you how "family friendly" they are during the recruitment process. No matter what the magazines and the rankings say don't expect that your firm will be on your side while you try to balance work and family demands.
In reality, law firms do very little in practice to help their associates and partners handle the challenges of working and parenting. The truth of the matter is that your firm is not your friend and it is not their job to make your life easier. I'm not trying to be a "Debbie Downer" - I'm trying to be as honest and realistic as possible. Once you start a family, you should expect to make hard choices about your career goals and aspirations. It may not be possible to "have it all" or "do it all" - there will be choices to be made and it is a matter of deciding what's important to you.
Once you decide what you want for your career and your personal life, talk to a trusted mentor at your firm and figure out how you can make it happen. You need to be an advocate for yourself and for your family.