With enough amount of light outdoors, you can keep up with the shutter speed even at low ISO, but indoor shooting is easy and seamless at higher ISO and the camera eliminates any noise.
"The EOS R5 also has incredible low-light capabilities and when you're working with kids, you'll often be outside for part of the session and then indoors so you need to be able to keep your shutter speed up and the ISO." With enough amount of light outdoors, you can keep up with the shutter speed even at low ISO, but indoor shooting is easy and seamless at higher ISO and the camera eliminates any noise.