I've never found baby Beavertail in the wild before, until now.
A full grown mature plant.
Each one of those little spots are called areoles where hundreds of tiny hair-like spines grow. The grouping of spines are known as glochids. Getting these into your skin you do not want to do.
They are very irritating although you do not immediately feel the irritation. It usually makes itself apparent an hour or so later. It is then I stop whatever I am doing and proceed to get the spine out with tweezers and a magnifying glass for the longer they remain the worse it will become.
I have a beavertail in my cactus garden at home. Every time I have got spines in my hand it wasn't from touching the plant itself. I got it from something else that had touched the plant. Now look at the third photo again and you will see where birds have sat on the edge and pooped and where somebody has nibbled away at two of the paddles. How do they do it?