Could my 5 weeks old chicks have bumblefoot

[little guinea]

I've noticed that a couple of my 5 week old chicks have a soft lump on the bottom of their feet. It looks like the early stages of bumblefoot
I don't understand, if it is the early stages, how they have got them. I bought them at a week old and they have been kept together in the conservatory in a large pen and i have cleaned the pen daily, providing them with fresh wood chip and straw, the floor is soft as the base layer is carpet then covered with a shower curtain (easy to clean) then the wood chip and straw.
I've got a few weeks yet before i will integrate them with the others but i'd prefer to have their feet in good condition before i do. Any suggestions??

 

[tamberlin]

Can you get a photo to show us?

 

[little guinea]

There is no scab as described in all the forums they're just soft lumps at the moment which i'm told is the very early stages. I can get a photo though i don't think it will highlight it properly