Ostensibly, Labour would punish criminals further than the Tories. They say "Labour will lock up dangerous child abusers." This implies that dangerous child abusers are not locked up already, but of course they are! This is classic spin.
It may be true that "Under the Tories, 4,500 adults convicted of sexually assaulting children under 16 served no prison time", but that doesn't mean that any of those 4,500 are dangerous child abusers. For example, one of them may be a 16 year old girl that's in a relationship with a 15 year old boy. Prison is not the only option.
So saying “Do you think adults convicted of sexually assaulting children should go to prison? Rishi Sunak doesn’t” is fatuous in the extreme.