Entirely personal question and ultimately you have to figure out what your priorities are (and how exhausted you want to be). Is it something that can be done different than something that should be done, are two separate questions. And not to mention 2 kids under the age of two!!!
I went back back to school for my MSN on the heels of completing my BSN. I had a 3 year old when I started. Coursework wasn't hard, but the clinical time nearly killed me. I was spending nearly 60-65 hours a week at the hospital and I had my second child just in my second to last semester. If I didn't have such a supportive husband and daycare, I wouldn't have made it. My only regret is that I missed out with my child during that time away then leading right into less attention for him with a new baby. I don't regret my choice but perhaps the timing. We are forged through our mistakes and our achievements. Good luck on what ever you decide.