focus – How can many children be photographed, so that not every face blurs?

You have to change the aperture. Catchment Renzen! Limit it a lot!

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

In addition, 105mm is a relatively long focal length to take pictures of many children, even if you look at your full screen sensor. You have to step back. In fact, you probably need to step back enough to hit a wall when in the house!

Nothing is impossible. Use a shutter of F / 10 – F / 16, and you will suddenly see that your depth of field is significantly better. For a full-frame camera, F / 16 is likely to work much better than F / 10. If you go back a step, you can also 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.

With such a portrait lens, image stabilization may also occur. At the focal length of 105 mm, this is definitely a problem. If you need to capture the picture really fast, it's better to use a narrow-aperture zoom with maximum aperture and image stabilization. Example of such a lens: Nikkor 24-85mm 1: 3.5-4.5G ED VR.

Obviously, when the kids move fast, image stabilization does not help freeze the movement.

(To edit: I originally suggested F / 5-F / 10, but after consulting a depth of field calculator, even such a large F-number as F / 16 can be problematic with this lens from a short distance. Due to the full-screen sensor and the long focal length, the depth of field is very limited.)