I could see children's toys and clothing being an excellent choice for affiliate marketing.  Tech and other electronic equipment should be a good fit as well.  Those options would be fairly simple to create content about, too.  It almost sounds too good to be true.  

I earn affiliate money through my forum about space tourism.  I mostly focus on vacation packages to our spaceport locations that are under development in the UK.  Sometimes I'll review a camera or other bit of tech that still fits my niche.  I don't earn loads from it, but a bit trickles in every month.