Heya, I have never seen anything like that apart from when I tryed a drop of jungle formula on the tip of a leaf to see what would happen.(to see if I could use it as repelant,, not just beacuse I was baked and just wanted to see what happen) The spot quickly died and then spread through the leaf to the stem. The leaaf just died and fell off. It never had a bright colour to it, Like those pics,,,]
I would just advice triming that leaf and removing it, incase it is somthing very bad. What time scale was this over? If it was within 24 hrs it is more likly to be a diease than anything else. Like I say by the time it got to the third pic I would have removed the leaf.
It could be systemic so Id keep a close eye on it. It looks like tree leaf diease,it affect just the leafs of conifirious(ones that shed leafs in winter) cant remember the specific name of it and have never herad of it affecting other plants, Some one on R.I.U, must know,,
Hope they read your thread,,
Hope your babies are ok, take it easy...