In all likelihood, the edges of the bayonet wouldn't have been particularly sharp. It would have been more a thrusting weapon. Remember, the bayonet's whole purpose was to turn an empty rifle into a makeshift spear (there are early training manuals detailing just how this is done). Depending on how deep the thrust was, it would have hurt like bejeebers, and undoubtedly left a scar, but would not necessarily have sliced and diced.
Depending on the age of the child and the area of the disrupted tissue, a limp would be entirely a matter of chance.
To stick my oar in the water as a relative outsider who isn't familiar with any of the parties involved here and has no dog in the hunt, there ARE useless people who'll ride a minor injury forever. (Fiddy Cent) There ARE people who'll beat a major injury to death with its own scar tissue (Teddy Roosevelt). Saying that is not the same as saying that ALL people who are disabled are useless weaklings, nor that ALL people who beat major injury are super heroes (although TR came pretty close).
While part of being civil is indeed not being thoughtless, part of it is also not reaching out to seek umbrage where none is offered. Reductio ad absurdum has no place in civil discourse.