Dear friend, welcome to HCM.
if the pain is not reducing after a week, you should get an Xray chest to look for any rib trauma (I personally feel it is much less likely with a punch from a kid ). could be a
blunt trauma to ribs .
more likely would be a trauma to the soft tissues of the breast.
A breast examination by your doctor and if necessary , un
ultrasound of the breast would help to see if there is any
contusion / collection of blood etc.
I do not think it is serious , but need to look for teh extent of trauma causing intense pain.. you can ask for injectable or continuous release pain killer patches for better pain relief.
keep the breast well supported till then and see if reduces pain.
I hope to have answered your query satisfactorily.
Take care and please keep me informed of your progress.
Good Luck !
May I request you to rate your experience here before you close.
Thank you.