Thank you for your query on Healthcare Magic,
As that hard bump is just below the center of the distal sternum
is is looking like xiphisternum which is the lower part of sternum as in some children the lower end of xiphisternum will be curved and the tip will be palpable as a pea sized tip and it will move with respiration. Nothing to worry, whenever your baby well baby visit is there you show it to your Pediatrician
and clarify your doubt.
I hope you got answer for your questio