I use the 24, 35 and 50 when shooting the kids, I used to own the 85 (a bunch of times) and it doesn't keep up with two-three year olds. The 35 L is my favorite, I like the contact you get with the subject with wide apertures and that focal, really pops. I have gotten a few fun, cool images laying on the floor with the 24 also. i recently bought a 24-70 mk1, and that is veryvery useful with kids, I set my desired focal and move my feet to frame instead of zooming to frame, that way you can control the perspective and best of all, change it in a split-second. I find the 70-200 also very useful (and I am a prime guy) and I see people mention the 135, I have also owned that a few times, but for ME I can't really find a place for it, it's too long or too short for me. The 70-200 on FF is awesome for all sorts of people shots.