focus – How to make photos full of children so that everyone is not fuzzy?

You must change the aperture. Reduce it! Reduce it a lot!

I do not think your portrait lens is a good idea to take pictures of many children. It is designed to scramble the background so that the viewer's attention is directed to the main subject of the photograph, the person photographed. If there are many children at different distances, you can not focus everything with the F / 1.4 aperture.

In addition, the focal length is long enough for shooting many children, even taking into account your full-frame sensor. You have to step back. In fact, you will probably have to step back so much that you will come up against a wall if you are inside!

But nothing is impossible. Use something like the F / 10 – F / 16 aperture and you will suddenly see that your depth of field will be much better. On a full-frame camera, F / 16 will probably work much better than F / 10. In addition, recoil will help you to increase the depth of field.

Use the aperture priority mode of your camera and set the aperture to a value between F / 10 – F / 16.

In addition, such a portrait lens may lack image stabilization. At the focal length of 105mm, it's definitely a problem. If you need to take the picture very quickly, honestly, you'd better choose a zoom kit with maximum aperture and narrow image stabilization. Example of such a goal: Nikkor 24-85mm f / 3.5-4.5G ED VR.

Now, if the children move fast, the image stabilization will obviously not help to freeze the movement.

(Edit: Initially, I had suggested F / 5-F / 10, but after consulting a depth-of-field calculator, a F-number as large as F / 16 could pose a problem with this short-range lens. The full frame sensor and long focal length greatly limit the depth of field.)