You need to change the aperture. Narrow it down! Narrow it down a lot!
I don't think your portrait lens is a good idea for taking pictures of lots of kids. It's designed to blur the background so that the viewer's attention is directed to the main subject of the photo, the photographed person. If there are lots of kids at various distances, you can't make all in focus with the F/1.4 aperture.
Also, 105mm is rather long focal length for taking pictures of lots of kids, even considering your full frame sensor. You need to step back. In fact, you probably need to step back so much you'll hit a wall if you're indoors!
But, nothing is impossible. Use something like F/10 - F/16 aperture and you'll suddenly see your depth of field will become much better. On a full frame camera, F/16 will probably work much better than F/10. Also, stepping back will help you increase the depth of field.
Use the aperture priority mode of your camera, and set the aperture to something between F/10 - F/16.
Also, such a portrait lens may lack image stabilization. At the 105mm focal length, it's definitely a problem. If you need to take the picture really quickly, honestly, you would be better off with a kit zoom with narrow maximum aperture opening and image stabilization. Example of such a lens: Nikkor 24-85mm f/3.5-4.5G ED VR.
Now, if the kids are moving fast, then image stabilization won't obviously help to freeze the movement.
(Edit: I originally suggested F/5-F/10, but after consulting a depth of field calculator, even as large F-number as F/16 might be problematic with this lens at close distances. The full frame sensor, and the long focal length make the depth of field very limited.)