My memory is fuzzy but I either had a bantam rooster with one leg who had issues with infected hocks, or a chick that had the same issue. I'd soak the chick's legs in a warm Epsom salt bath to help with pain, infection and swelling, and look toward getting some antibiotics and/or painkillers into him. You can easily look up appropriate medications and their dosages for chicks. If the chick looks like he's irritating the wounds by walking on them I'd suggest covering them or building him a "chick chair".