Welcome to HCM!
The swelling you describe may be one of the following:
1-enlarged groin lymph
Is there any skin lesion on the leg or foot of that side?
2- localised infection staring as a bump.
In this case there may be some tenderness or redness
around the area
3- it can be a small hernia
This will be reducible non tender and no redness around.
Show the baby to the pediatrician
Nothing to worry!