What can be more niche than Lice? When you have the knowledge
it could be a good idea. You will not be the first one but

Lice Treatment Center has done it already
but that should not be a big problem.

What I like about this idea is that you could ship these
products very easily. Also there is not that many competition.
With a good Magento webshop you could have this business up and
running in no time.

The Magento design would need to be clean and simple.

Clean because you are selling health products. Health products
need a clean webshop or you will not sell that much. I would
not buy health products in a real shop if the walls where black
or dark red.

A simple design with just enough pages about the Lice business
would get you up and running in no time at all. You could a
removal service or only sell products. You could contact
schools and other institutions that have many children.