We have a small kitten---maybe 4-5 weeks old--she has a rounded swelling on her lower abdomen, about the size of a quarter.
It doesn't seem to bother her---when I pressed on it there was no pained reaction.

What are we dealing with here?

Thanks!

It could be an umbilical hernia.

An umbilical hernia?

What needs to be done, if anything?

It will get fixed when the kitten gets spayed. Just monitor it for now and bring it up to the vet when she goes in for her first vaccines in a few weeks.