um [tentative] actually, it is presumed innocent until proven guilty.
Nothing changes whether they were guilty or innocent, it is just that UK law expects us to presume they are innocent regardless, until something is proved one way or the other. If someone accused of something actually did it, they are still guilty, just presumed innocent.
All a jury can do is decide whether or not to convict. They can't change the actual guilt.
I feel very sorry for all involved, as it is a terrible, terrible event. I really hope that the police and courts do a good job on this one. Nothing can bring those children back, but I hope the case is solved quickly and cleanly, with the right verdicts.