thank you for posting your query in healthcaremagic.com.... well it looks like a mild bacterial infection following the prick and thats why it is swollen and red....make sure there is no part of the pricker left inside the skin...then do the following- keep the area clean apply mupirocin( t-bact) ointment twice daily on the area after cleaning the are properly you can continue benadryl if there is much itching but mupirocin should be sufficient... provide some rest to the foot you can also give hot compress twice daily if it does not reduce in 3-4 days, you can take him to a doctor.... hope this was helpful... contact me for any further queries.... regards