Suggest Remedy For Lumps In Foot

My son has had a small 2x2mm skin coloured lump on his foot for a while. Today my husband said it looked as though it had a pimple head on it and he squeezed some pus out of it. I took a look at it several hours later and it looked as though there was more pus. When I squeezed it only a tiny bit of pus came out but...this is difficult to describe...but it looked as though his skin turned inside out and a mushroom shape appeared on his foot. The lump now looks as though it is a wart. There was no blood present. Any ideas??? Your advice would be greatly appreciated.