Weeding for Kids - hand sickle?

I have four boys.  The oldest uses the reel mower, and the 6 year old really loves our full-length "weed cutter" - it is sharp enough to damage small trees (guess how I know. . .) but has a very hard time with grass and false dandelions.  

I am wondering if the new Hand Sickle would be safe enough for my 6 year old to use.  Or do you Permies have any better suggestions for dealing with the hard-to-get borders that the reel mower can't?

My 4 year old really likes to wield our hori-hori (narrow digging spade with a serrated side) as well as a mini-maddox type thing. He doesn't really use them very effectively but he enjoys it