Thanks for writing in.
As from the description of lesion it looks like insect bite, you can apply calamine
lotion at affected site. If it is insect bite it will resolve in few hrs.
But it still persists with increasing pain, you need to consult pediatrician
for ruling out internal injury
.[ because there is history of squeezing by brother]
In that case you may need ultrasound
to know exact injury.
I hope this information helps you.