Thank you for your query on Healthcare Magic.
Your child might have developed a hematoma
and bruising secondary to the injury
For pain you can give Motrin
in prescribed dosage.
The lump is due to formation of hematoma due to collection of the blood.
of the underlying rib bones has to be ruled out by the physical examination of the child by a doctor and by doing X-ray.
If it is hematoma it will take 5 to 7 days to subside.
Therefore I advise you to consult the doctor for the examination and treatment.
Hope I have answered your query.