There are many ways to arrive at the truth.

Ask: "Why did you hit your brother?" (Don't ask whether he hit his brother if you were standing there watching it happen; why give the kid a chance to lie and make it worse?)

Gather evidence. Pick up the broken pieces of flashlight. Let the neighbor kid attempt to reassemble the flashlights. Send a sibling for frozen vegetables. (What, you thought you had actual ice packs in the house? Those were used for science experiments years ago.)

Speak very calmly.

After a while, come up with the brilliant plan to ask the combatants for "written accounts" of the event. These accounts will be funny and sad and will include accusations of everything from poor hygiene to communism. Really.

(Leave the written accounts on the kitchen counter and the oldest sibling might come by and edit them for grammar and spelling.)

Think about your parenting for a while. Don't forget to think about Cain and Abel. At some point in your musing, decide that it's really important to you to remember which one killed which and go do a google search instead of trying to come up with an actual print version of Genesis, which wouldn't be all that hard to do, right? Try to decide whether the fact that the first two google hits refer to Microsoft products is the first sign of the end times.

Talk to the boys. You can load the dishwasher while you talk; it makes things seem more … ordinary. Don't forget about the frozen vegetables. They get mushy fast and then you'll worry about botulism, and really, who needs to be thinking about botulism at a time like this?