It looks like a fungus infection.
Big toe nails have different color and texture from the rest of the toes
There can't be another toe nail under it. Its just flaking off in layers which is either a sign of fungus, infection, or vitamin deficiency. Don't freak out, don't let us scare you lol it can all be fixed! I would start with over the counter fungus medication on his toe nails first. Take him to the Dr, see what they say, ask about the dosing for his size
My LO was vitamin deficiency as he is so hard to try and get to eat! And our health visitor mentioned the vitamins and since then there's been no issue with his toe nails
The same happened to my little one a few months back, it was hanging off then he caught it and it was bleeding, he doesn't let anyone touch his feet or hands but I distracted him and cut the excess off then the bit I couldn't get to fell off on its own xx