I am looking for some new lens recommendations. I have a D7000 with Sigma 10-20, Nikon 18-105, and Nikon 70-300. I also have an SB-800. We have a newborn on the way later this year and I am looking to get one or two faster lenses. I am debating between a 2.8 mid range zoom (Nikon 24-70) and a prime lens setup. What would you guys with children recommend me in my situation? I have no issues buying used if that makes a difference.