A less drastic solution, possibly...

So today I was in the kitchen rinsing out some dyed stuff in the sink when Olivia comes in, streaming tears. "What's the matter?" I finally, finally get her to speak, and she says "look what happened to my fringe (bangs)". I look, and notice it's a bit shorter than it was, and not quite so even. She has two friends over, so I immediately suspect hairdressing games, even though we've made it quite clear that there is to be NO haircutting. Anyway, I finally get out of her that it was she herself who cut the fringe, not Nina or Gabriella, which is good in a way, but bad in another way. "Why did you cut your fringe, darling, you know you're not supposed to use scissors on your hair..." "Because it was all sticky, Mummy, from the Golden Syrup" (they'd been eating waffles earlier). I literally had to stop and take a deep breath. "Olivia," I said, "Don't you think it would have been a little simpler just to wash it a bit?". Luckily, after being trimmed up by Mummy a bit, it looks ok, just a little shorter than normal. At least it was her OWN hair.