If they're only 6 weeks old it's very odd, isn't it? Are you sure the lumps won't soak off? A friend if mine once bought a quail out of pity because the seller said the cherry-tomato-sized lump it had on its foot was a tumour. She soaked and bathed the foot and it came off, it was a poo ball, and the bird was fine.
How long have your quail been on the mesh? Presumably you had them on a flat surface when they were chicks and it's very difficult to keep their feet absolutely clean. I know from experience how anything chicks tread in ends up as a solid mass on the feet, which collects more and more if left unattended. Though as I said I would expect it to be on their toes rather than their legs. Have any of them got these bumps on their toes, or anywhere else?
You could try giving a good soak in warm water. Get a small basin of comfortably warm water, hold the quail with your hand over its wings and gently dip the legs in the water. Hold it there for a while, then try gently rubbing the bump between your fingers. You may need to keep repeating this as if the bump is at least partly dried poo it will be hardened and fairly insoluble. Be careful not to injure the legs but see how much you can dissolve or gently pick away. It may help to use a cotton bud to work on the legs, and a little salt in the water as disinfectant would perhaps be a good idea as well. It will take a while but if it will come off, you'll have to do it to all of them.
Are these your only quail? If you have others, are they unaffected?
