Hi, Akshay, this is Akira mentioned by Airy.
I used to use AF-S 50/1.8G on both D610 and D750. Df shares the same AF system with D600/610, and the AF system of D750 is noticeably better in terms of the size of AF area, low light performance, accuracy, speed and immunity to the IR emitted from the incandescent lights.
However, even the AF system of D750 may not be fast enough to chase toddlers when combined with AF-S 50/1.8G. As Airy notes, the 24-70/2.8 zoom should focus faster. AF-S Micro 60/2.8 can focus quite fast.
Although AF-S 50/1.8G is not the fastest lens to focus, it is an excellent all-rounder. It is sharp enough wide open, its bokeh is pleasing, it is very hard to induce flare or ghost. You will not regret having purchased one.