Hello!
I'm not too sure how old your children are, but are they of the age that you can tell them something and they'll take it in? Could you perhaps tell them that they're not to go too close to the water unless they're with you. Presumably they're never unsupervised near the pond anyway, so it shouldn't be a problem. I'm all for keeping tiddlers safe, but I think to introduce something that will visually detract from the beauty of a pond might not be the solution. When I was a wee nipper, my Mum told me never to touch the 'Purple' flowers (Nightshade) and I never did. She told me about the dangers and instead of her ripping down the plant and ridding the garden of it, she told me about it.
I appreciate fully that children are inquisitive and curious, and that's why we love them!
I think that sometimes, things can be compromised. It's totally up to you obviously, but do tell us what you do
Nick