I noticed when you initialize a new project the boilerplate App.js component has:

<h2>Welcome to React</h2>

This is semantically incorrect since h2 implies a 2nd level heading but there is no parent h1.

Recommendation: Change heading to use h1 tag:

<h1>Welcome to React</h1>

Reference for accessible headings: http://accessiblehtmlheadings.com/